Iodometric titration on paper device #PADs

Titration technique is widely used in various analytical service providing and teaching laboratories. In this technique, a solution of known concentration is used to determine the concentration of an unknown sample. The currently used titration methods consume large volume of reagents and samples (hundreds of milliliter) and glassware like burette and pipettes.

Design of iodometric paper test card (source)

Titrations now can be carried out in a piece of paper modified with appropriate reagents. Professor Lieberman's group from University of Notre Dame recently has described an iodometric titration method in a paper card-published in Analytical Chemistry journal. Titration in the paper test card starts by applying a test solution to the test card in which multiple dried reagents have been stored separately. The reagents reconstitute and combine through a surface-tension enabled mixing (STEM) after the application of unknown solution. The end point of the titration is indicated by the appearance of blue complex of iodide and starch. The signal can also quantitated by using image-processing software.

Iodometric titration involves a redox reaction used to determine the amount of variety of analytes of interests. The authors used this method to quantitate the iodine present in common salt and also demonstrated the versatility of the titration device by quantifying beta-lactam antibiotics via an iodometric back-titration. In later example, the antibiotic was degraded in base to obtain a redox active thiol. The reaction mixture was then acidified and a known amount of excess triiodide is added to oxidize the thiol. Ureacted triiodide is back-titrated with thiosulfate.





Unique feature of the iodometric test card is its ability to store multiple reagents separately for long time and allowing them to mix and react when desired.


The paper titration technique would be very useful in developing countries and in remote locations-especially. It is cheap, easy to perform and requires small amount of reagents. Also, generates less waste. Authors described the stability of this test card (stored reagents) for ~20 days at temperature 40deg C. It is not clear if the results obtained at above conditions will be valid for more than 20 days and higher temperature combined with humidity. Lets consider a village in India. Some of the Indian villages see temperatures more than 40 deg C (easily 45) that combined with high percentage of humidity. Will the test card work in this location? Proper packaging can protect effect of humidity, however. If the test card is not manufactured at local level, then 20 days time frame is not enough. It will take months for the cards to be used in field.

This method has great scope to be introduced in to the classroom-teaching labs.




Will this new method replace traditional ways of doing iodometric titrations?

Acid-base titration on paper microfluidic device: will it replace traditional acid-base titration?

u-PAD for acid-base titration (source)

Research in paper-based microfluidic analytical devices (u-PADs) has evolved very fast in past couple of years. Recently, scientists from Okayama University, Japan have reported a technique to carry out acid-base titrations in PADs and the work has been published in journal Analytical Chemistry. 

The wax printed u-PADs consisted of ten reaction (acid-base reaction) and 10 detection reservoirs. The detection reservoirs were applied with a constant amount of phenolphthalein (indicator) and the reaction reservoirs were applied with various amount of a primary standard potassium hydrogen phthalate (KHPth). Only less than a microliter volume of the solutions were needed. The base (e.g., NaOH) was dropped onto the center reservoir of the device. As the base wicked towards the reaction reservoir, it then reacted with the acid and if any extra NaOH remained it then moved further and reached to the detection reservoir to produce a pink color. The number of detection reservoirs with no color change was used to determine the concentration of NaOH. The authors have tested this technique using other acids like nitric acid, hydrochloric acid, sulfuric acid, and acetic acid.

Acid-base titration is widely used in teaching chemistry  and in variety of analytical services. The currently used titration methods involve large volume of reagents and samples; glassware (burette and pipettes).

The new u-PAD being used in field testing (source)

The new method takes only about a minute to complete the titration and is more advantageous than classical titration methods in terms of speed, portability, and disposability.

Eventhough the micro-titration device was shown to be stable for couple of days, it requires further improvements to make the device stable for longer time. The reagents stored in the PADs degrade with time. Therefore the reagents have to be applied at the time of use only. Also, temperature plays bad role for the stability of the PADs. Therefore not suitable for places with higher ambient temperature (e.g., summer time in India).

As PADs are cheap, this new titration technique may replace the traditional titrations, specially in developing countries. Teaching settings can immediately adopt the technique.

new trends in the application of paper based analytical devices

Recently, I went to ACS Fall 2013 National meeting in Indianapolis. I presented two talks. My first talk was about a new microfluidic based ELISA (enzyme linked immunosorbent assay) method for measuring very low concentrations of protein markers and it was in a session called "portable instrumentation for chemical analysis". My second talk was about a new kind of enzyme substrate for ELISA applications and was in a session called "capillary and microfluidic platforms for bioanalytical measurements". Both sessions were under analytical chemistry division. 

As I am more interested in paper based devices these days, I attended talks on low cost analytical devices primarily based on paper. Some talks by professors/students and more posters. I believe the research presented there will be seen more and more in future. Let me point out some of them.

1. paper based devices to monitor low quality pharmaceuticals and iodizing agents in salt.

PBAD used for testing pharmaceuticals. source: ACS

Professor Marya Lieberman and her group from the university of Notre Dame have developed paper based testing devices based on simple colorimetric chemistry. These devices are used to detect low quality pharmaceuticals, iodizing agents in salt etc. They have used these devices in really a low resource settings like in Kenya, Haiti, Iraq, India etc. The idea is that these devices can be sent out to every house/village to test whether the medicine (commonly used) contain what they are supposed to contain. In developing countries this is a very big problem. Prof Toni Barstis's group from Saint Mary's college is also working on paper based colorimetric devices that distinguishes between genuine and low quality anti-malaria ACT (artemisinin combination therapy) medications. The same group has also focused on identifying counterfeit drugs for river blindness.

2. paper based devices for detecting microorganism like bacteria, fungi etc.

One group in Canada are developing paper based culture devices for bacteria. Professor Carey's group from Taiwan are working on single step colorimetric sensing of human pathogenic bacteria in blood.  Their paper device has an array of several dyes (proprietary) that give a signal when reacted from different metabolic by-products of bacteria. This produces kind of finger print to identify bacteria. When successful, this technique could come to market for regular bacteria assays. click here to see their recent publication. Similar to the work by Dr. Carey's group, a group from the University of Illinois at Urbana-Champaign have worked on differentiation and identification of pathogenic fungi based on colorimetric sensor array that reacts with the volatile organic compounds produced from fungi.

no-instrument measurement in paper-based device

Paper-based devices (PBDs) have emerged as a new class of inexpensive devices with potential use in medical diagnostics, environmental applications etc. They are not only inexpensive but also proven to be sensitive, quantitative, and reliable in many applications.

The colorimetric detection is one of the popular methods of quantitation of analytes in PBDs. Color developing reagents are used on the micro-reaction chambers on paper. The color developing reagent then reacts with the analyte of interest when the later is applied specifically and quantitatively. Simple and widely available instrumentations like a office scanner or a camera (could be a mobile phone camera) are used to capture the color which is then quantitated by measuring the signal using image processing software.  If you don't have camera and/ or image processing software, don't worry. Scientists from Colorado State University have developed even a simpler method to quantitate analytes. This interesting work has recently been published in Lab on a Chip Journal.

The new technique relies on the length of the color developed. They call this as a simple distance-based detection. You just need a ruler to quantitate the analyte concentration: no camera, no scanner, no software.

How does this work?

1.

First of all create a paper-based device. In their work, they have used wax printing to make PBDs. Their design has a straight channel, like a thermometer. There is one circular reservoir at one end. This reservoir is used for sample addition and/or transfer of analyte to the detection zone (long conduit).

2.



Colorimetric detection reagents are deposited along the flow channel. They tested two different methods for this purpose: spray application or pipetting. Once the reagents are dry, the device is ready to use.

3.

Sample solution in water is then added to the sample reservoir which flows into the detection/flow channel. The analyte reacts with reagent and develops color. Once all of the analyte is consumed, the color development stops. Analyte quantification is then done by measuring the length of the colored region in the detection zone by a ruler.

Authors of this paper have demonstrated their technique by measuring three different analytes: nickel, reduced glutathion, and glucose.

This new measurement technique is claimed to be accurate and sensitive compared to conventional methods.

In this figure, you can see that higher the concentration of analyte-the longer is the color developed region in detection zone.

Affordable diagnostic tests for health problems

JUST A DROP: This paper-based test, which costs less than $0.10, could help health care providers in developing countries monitor for liver toxicity associated with HIV and TB treatments.COURTESY OF DIAGNOSTICS FOR ALLPaper based devices getting popularity.

Human immunodeficiency virus (HIV) and tuberculosis (TB) are two of the leading killers in the world, taking an estimated 1.7 million and 1.4 million lives each year, respectively. The worldwide distribution of medications to treat these diseases has been a boon to global health, but some of those drugs can cause liver toxicity, so patients taking them need routine liver monitoring.

In developed countries, that’s simply a matter of visiting the doctor’s office and having blood drawn. With a whiz in an electric centrifuge and a quick pass through an automated machine to detect liver metabolites, the results are in. But in developing countries such as Botswana and South Africa—areas plagued by HIV and TB infections—such tests are virtually nonexistent. And there are no alternatives. “In a resource-limited setting, monitoring isn’t happening at all,” says Nira Pollock, associate director of the Infectious Diseases Diagnostic Laboratory at Boston Children’s Hospital. In some cases, undetected liver damage can lead to organ failure and death.

Three years ago, Pollock joined forces with a local Massachusetts biotech company called Diagnostics For All (DFA) to develop a paper-based method for diagnosing liver damage that uses just a droplet of blood. The test was unveiled in September 2012: a square of paper the size of a postage stamp that costs less than $0.10 and measures liver damage with 90 percent accuracy in just 15 minutes (Sci Transl Med, 4:152ra129, 2012). DFA is now analyzing field-test data from 600 patients taking HIV and TB medications in Vietnam, and hopes to apply for regulatory approval in Europe and the United States within the next 1–2 years, says Jason Rolland, senior director of research at the company.

The test has the potential to reduce deaths associated with liver damage in the developing world, and is just one of a handful of new products aimed at bringing affordable, easy-to-use diagnostics to low-resource settings. DFA is using its technology, which takes advantage of the natural wicking ability of paper, to create cheap paper-based assays for preeclampsia and anemia in pregnant women, bacterial contamination of cow’s milk, nutrient deficiency in children, and more—all for pennies per test. Other companies are taking advantage of the near ubiquity of mobile devices, developing a smartphone eye exam, a flashlight that measures diabetes risk, and a tablet app that monitors both heart health and water sanitation.

To increase access to health care in the developing world, “we need a fundamentally different class of diagnostic devices—ones that are robust enough to be used in the field and simple enough to be used by midlevel professionals,” says Sailesh Chutani, president and CEO of Mobisante, a Washington State-based biotech that sells a smartphone-based ultrasound system. “I predict we’ll see more and more of this style of device. It is the only way to get a handle on the global health situation.”

The greatest need

Low-cost, point-of-care diagnostic tests are not new. Today there is a range of simple, rapid HIV assays available, including those that can detect HIV antibodies in whole-blood specimens (no blood processing required), as well as rapid diagnostic tests for malaria that produce results in only 15–20 minutes and require no laboratory or even electricity. In the 10 years since these tests became widely used, they have transformed the management of HIV and malaria worldwide. They have also fueled an industry aimed at making similar low-cost diagnostics for other health burdens in the developing world, including the winner of The Scientist’s 2011 Top 10 Innovations contest—a $10 holographic microscope designed for use in remote locations.

“Not all innovation needs rocket science,” Margaret Chan, director-general of the World Health Organization (WHO), said at the opening session of the 2012 Pacific Health Summit in London. “Given the world’s most pressing health problems, the true genius of innovation these days resides in simplicity.”

GOING DIGITAL: This smartphone ultrasound system is one of a growing number of diagnostic devices that take advantage of near ubiquitous mobile technology.COURTESY OF MOBISANTETraditional tuberculosis testing, for example, includes X-rays and blood tests, both of which are resource and training intensive. The simplest TB diagnostic currently on the market is a sputum smear test, which uses visual detection of TB in a sample of coughed-up mucus. An accurate diagnosis still requires a microscope and trained personnel to identify the bacterium, however. As a result, millions of individuals around the world have undetected, and therefore untreated, TB infections. And the WHO estimates that every untreated individual will spread the bacterium to 10–15 people each year.

Global BioDiagnostics Corp., a Texas-based start-up founded in 2009, is one company pursuing a TB solution, based on research funded by a Bill & Melinda Gates Foundation grant. Recently, Global BioDiagnostics’ founders at Stanford University and Texas A&M Health Science Center demonstrated the ability to detect a minute amount of TB—fewer than 10 bacteria in a sputum sample—using an engineered molecule that fluoresces when cleaved by a TB enzyme called BlaC (Nature Chem, 4:802-09, 2012). Global BioDiagnostics is now moving that proof-of-concept experiment into a full prototype test, which will require “no complex processing steps, no handling or pipetting sputum,” according to President and CEO Michael Norman. A $2,000 fluorescent reader will be required to measure the results, but each TB test is estimated to cost just $5 or less.

Other companies are turning to a new plague of the developing world—chronic diseases. “There is a huge upturn in chronic diseases—epidemics in diabetes, cardiovascular disease, and even cancer—that are now overtaking traditional global health diseases such as malaria,” says Bernhard Weigl, principal investigator at the PATH Center for Point-of-Care Diagnostics for Global Health.

To address this concern, PATH, a nonprofit global health organization that has already developed numerous low-cost diagnostics, is now evaluating two diabetes diagnostics: a quick strip test to diagnose gestational diabetes and a noninvasive diabetes-risk screening procedure. Diagnosing gestational diabetes traditionally requires 8 hours of fasting, a blood draw, and at least two doctor visits for pregnant women. PATH hopes to replace that ordeal with a quick-and-easy strip test that costs less than $3 and requires just a drop of blood. And a second test, under development by Netherlands-based DiagnOptics and New Mexico-based VeraLight, can assess diabetes risk by simply shining a light on a person’s forearm. PATH is currently testing the machine—which records fluorescence emitted from proteins in the skin, indicating the level of sugar in the blood—in clinical trials in India. Weigl hopes the assay will encourage at-risk individuals to take appropriate action to prevent the disease and will cost less than the common diabetes blood test, which runs about $65 per test at a doctor’s office.

“It’s the functional equivalent of a blood-pressure cuff for diabetes,” says Weigl. “Now we can screen large numbers of people relatively cheaply without any invasive procedure.”

There’s an app for that

To keep costs low, some companies are turning to mobile device technology that is becoming ubiquitous the world over. Washington State-based Mobisante, for example, opted to use a smartphone as the backbone for its handheld ultrasound system, which performs scans at a range of frequencies that allows evaluation of many types of tissue. The device, which costs $7,500 including the phone and ultrasound wand, was used in Joplin, Missouri, to help diagnose injuries of the victims of the 2011 tornado and has been used at the Everest Base Camp to screen individuals for pulmonary edema. Last year, the system became the first smartphone-based diagnostic device approved by the US Food and Drug Administration, and the company is currently building partnerships to move it into developing countries, says CEO Chutani.

Another smartphone-based diagnostic that could soon hit the market is a pocket optometrist. Massachusetts-based EyeNetra has developed a $2 plastic lens attachment that snaps onto a smartphone screen and a mobile phone app that gives simple instructions for measuring nearsightedness, farsightedness, and astigmatism. This portable eye exam, which emerged from the Massachusetts Institute of Technology’s Media Lab, could help as many as 2.4 billion people worldwide who need glasses but do not have them, says Vitor Pamplona, cofounder and chief technical officer of EyeNetra.

Also in an effort to keep costs down, diagnostic companies are working to develop tools that can be used directly by patients, bypassing the trip to the doctor’s office. EyeNetra’s device, for example, comes with a simple tutorial and connects to a network service, so that a patient can self-administer the vision test and send results straight to an eyeglass store or ophthalmologist. Similarly, Mobisante’s smartphone ultrasound device connects to wireless networks in order to save images in the cloud and e-mail them directly to a doctor. And DFA hopes its liver toxicity test will someday be a home test, allowing patients to apply a drop of their own blood to the paper diagnostic, snap a picture of it, and send the picture to their physician.

THE DOCTOR IS IN: The Swasthya Slate health tablet provides multiple diagnostics and decision support systems for frontline health workers in India.COURTESY OF UTSAV SHARMAAt the Public Health Foundation of India, health systems engineer Kanav Kahol and colleagues are even hoping that their easy-to-use diagnostic tool, the Swasthya (meaning “health” in Hindi) Slate, will boost the local economy. The Slate is a book-size machine that wirelessly communicates with an Android tablet and includes a bag of plug-and-play sensors that measure blood pressure and levels of blood sugar and hemoglobin, conduct electrocardiography (EKG) tests, and assess water quality. The $350 Slate, including the mobile tablet, is already in use by health-care workers in several southern Indian states. The ultimate goal, says Kahol, is to distribute the device to mobile health assistants, who pay just half the cost while the government picks up the rest of the tab. “Then these guys have a self-employment model, where they can offer these services from home to home for a small fee,” says Kahol.

 

A worldwide solution

While low-cost diagnostics could revolutionize health care in the developing world, there is one major hurdle to bringing these products to market—money. While the products themselves are cheap, development isn’t. “The problem is almost always funding,” says PATH’s Weigl.

 

In order to fund a product, some companies look to first sell their device in North America and Europe. The same traits that make a diagnostic appropriate for the developing world—low cost, portability, ease of use— also make it attractive to developed markets. Mobisante, for example, has sold its portable ultrasound device to community clinics and large hospitals in the United States. “Our initial goal was to focus purely on emerging markets. But we realized is that is hard to do, so we found some niches here to get us started,” says Chutani.

EyeNetra also expects to cultivate a market in the developed world. “There is a clear need in the developing world for eye-care diagnostics, but in the developed world, the device also solves a comfort problem for people who don’t want to go to the eye doctor,” notes Pamplona. “We are going to make sure that we target both situations.”

Even a simple technology such as the DFA liver test could be used in developed countries as a way to conserve resources, says Pollock. Of course, “the first priority is the resource-limited setting,” she emphasizes. “We want all people to now have access to the same standard of care as people in a resource-rich setting.”

From The Scientist

Paper Devices research Moving Forward

University of Notre Dame chemistry professor Marya Lieberman and graduate student Abigail Weaver spent a week in June in Eldoret, Kenya, going from office to office in a regional hospital meeting people involved with pharmaceutical purchasing.

In hospitals like the one they visited, vigilant purchasing agents have to be on the lookout for counterfeit pharmaceuticals, but they often lack appropriate equipment to assess drug authenticity. Lieberman and Weaver develop paper-based microfluidic devices that can do such tests.

Hospitals like the one in Kenya “don’t have lab space,” Lieberman says. “There’s not even space to set up a suitcase lab.” In that type of environment, paper-based instruments can come in very handy. “We would whip out our paper devices and do tests right there on their desktops,” she says.

Lieberman ticks off the reasons people want to use paper devices. “They’re cheap, transportable, disposable, cheap.” She pauses for a beat. “Have I mentioned that they’re cheap?”

Lieberman is just one of a growing number of scientists who are turning to paper as a platform for microfluidic analytical devices. She and others were attracted to the field after reading George H. Whitesides’ first paper on the topic, published inAngewandte Chemie in 2007 (DOI: 10.1002/anie.200603817).

A varied cast of scientists is pushing the field forward, some by developing and improving paper-based microfluidic devices and others by using the devices for specific assays. The desire to run point-of-care medical diagnostic tests in limited-resource settings drives much of the work in this area.

For example, Paul Yager, a bioengineering professor at the University of Washington, Seattle, was already trying to develop low-cost diagnostics when he heard about paper-based devices. At the time, he was working on a project funded by the Gates Foundation to develop permanent instruments with disposable cartridges. The Bill & Melinda Gates Foundation would fly its grant recipients to annual meetings in locations where such devices might actually be used.

“They would take us out to real situations, real clinics, real population centers in the developing world—places that I frankly hadn’t been to before,” Yager says. “You’d get to chat about things like their actual budgets and the real issues and the most pressing problems. After five years of exposure to that, I reached the conclusion that the cost per test had to be way, way down, below what I still think the cost per test is going to be with the kind of technology that was being developed with a permanent instrument.”

But cost was only part of the problem, Yager adds. “Permanent instruments are a pain to use in the developing world. If you’re lucky, they sit someplace and stay plugged in. If you’re not lucky, they break or wander off, and you lose your ability to run them. It’s not easy to get a service call and, depending on where you are, not all that easy” to pack an instrument and have a shipper like FedEx pick it up for off-site servicing.

With paper-based devices, such worries disappear. Paper-based devices often don’t require power supplies. Many of them can be read by eye or with a camera phone—a common tool in the developing world.

Lieberman’s group and teams at other academic institutions with which they collaborate—led by Patrick J. Flynn and Holly V. Goodson from the University of Notre Dame and Toni L. O. Barstis from Saint Mary’s College, in Notre Dame, Ind.—develop chemical tests for counterfeit pharmaceuticals.

“We’re trying to put together libraries of color tests and get them all to play nicely with each other,” Lieberman says. “We’re also making a smart material, where information on how to add the reagents is stored in the paper matrix and the test output can be read like a color bar code.”

For pharmaceutical identification, each device has several lanes that detect certain functional groups, such as primary amines or phenols, in an active pharmaceutical ingredient. Lieberman also looks for approved or unauthorized excipients (inert ingredients). Color changes in the various lanes indicate the presence of particular components.

“These are chemical tests, so you have to be careful in interpreting them,” she says, noting that the tests are not yet sufficiently quantitative. The main bar to quantitation has been the difficulty of developing a reliable method of dosing. For ease of use, “we made a decision not to grind up tablets and make volumetric solutions,” Lieberman says. Instead, she and her coworkers simply swipe pills across the graterlike sampling region of the device.

They are working on the grater to make the device more quantitative. Nonetheless, the device is quantitative enough that during a workshop in Kenya it was able to reliably distinguish pure amoxicillin from amoxicillin that had been cut 50/50 with maize meal.

The current iteration of the test has 12 lanes, a sufficient number to identify the four frontline tuberculosis medications individually or in combination tablets of two or four drugs. The 12 lanes can be used to detect all four drugs individually, all seven possible binary combinations, and the quaternary combination.

In the medical diagnostics area, a device to perform liver function tests from the nonprofit corporation Diagnostics for All (DFA), based in Cambridge, Mass., is closer than any other paper-based device to working in the real world. The company holds an exclusive license to a number of patents from the Whitesides lab.

The test measures the levels of two liver enzymes—aspartate aminotransferase and alanine aminotransferase—and provides a colorimetric readout, says Una Ryan, DFA’s chief executive officer. By comparing the readout with a color guide, medical personnel can categorize the test results as normal, worrisome, or requiring immediate action.

DFA’s contribution has been to take academic ideas and turn them into real products, Ryan says. Most important, she adds, is that the tests are reliable and reproducible.

“It doesn’t matter how cheap something is. People won’t use it if it’s not reliable,” she says. “In the developing world, people don’t use diagnostics more often because they’re too expensive and not reliable.”

The devices currently made by DFA are stable for at least a year in high-temperature, high-humidity environments, Ryan says. The devices are now being tested at a Harvard University-affiliated AIDS hospital in Ho Chi Minh City, Vietnam. The hospital has a high incidence of hepatitis as well as AIDS, meaning that there is a substantial patient population with compromised liver function, making it possible to study whether the device measures what it’s supposed to measure. A 700-patient trial is ongoing.

DFA has developed a semiautomated process for manufacturing the devices, but the biggest hurdle to widespread use is what Ryan calls “the last mile”—distribution. Organizations like DFA can work easily with national or regional governments, but getting devices to people who work in rural communities “requires a lot of skill and good relationships,” she says.

DFA’s liver function test has not yet received regulatory approval. Most countries in the regions DFA is targeting accept both U.S. and European regulatory approvals. DFA will first apply for the CE mark, which denotes compliance with European regulatory standards. After that, it might also seek approval through the U.S. Food & Drug Administration’s 510(k) regulatory process for medical devices.

A growing number of academic researchers are working on ways to extend the capabilities and improve the assembly of paper devices. For instance, Scott T. Phillips and coworkers at Pennsylvania State University have incorporated fluidic batteries directly into paper-based microfluidic devices (Lab Chip, DOI: 10.1039/c2lc40126f).

In many conventional detection methods, like fluorescence assays, you need a source of power, Phillips says. “In really resource-limited environments, button batteries may be too expensive or have disposal hazards. We’re asking the question: Can we generate the power directly” in a paper-based device?

Phillips and his coworkers are helping answer this question by making multilayer batteries with electrolytes, electrodes, salt bridges, and conductive connections. Using AgNO₃ and AlCl₃ electrolytes, they constructed galvanic cells that can be connected in series or parallel and that produce enough current to power a light-emitting diode.

Phillips’ group recently devised a way to simplify the assembly of multilayer paper-based devices. Rather than alternate paper and tape layers, as is commonly done in the construction of such devices, Phillips and coworkers use spray adhesive to stick the layers together (Lab Chip, DOI: 10.1039/c2lc40331e). “The quantity of glue we are using to put two pieces of paper together is sufficiently small that it doesn’t seem to affect the wicking or wetting properties of the paper,” Phillips says. And the process is rapid enough that a single researcher can assemble hundreds of devices within an hour, he says.

Another group uses origami—Japanese paper folding—to craft multilayer paper-based devices from single pieces of paper. When Hong Liu, a graduate student in Richard M. Crooks’s group at the University of Texas, Austin, who grew up in China, first saw multilayer paper-based devices, they reminded him of origami objects he had assembled in childhood art classes.

Crooks’s group incorporates electrochemical detection into its devices by screen-printing electrodes on single pieces of paper and then using origami to fold them into multilayer operational units. Current devices have carbon electrodes, but he and his coworkers are developing devices with gold electrodes to make it easier to immobilize probe molecules on the devices.

They plan to use the origami devices for assays that test immunization status—for example, to identify children who have been immunized, even if their immunization card has been lost.

[+]Enlarge

 

LIVER TEST

These paper devices measure levels of the liver enzymes aspartate aminotransferase and alanine aminotransferase as well as positive and negative controls. Each device is 1 square inch.

Credit: Diagnostics For All

Not everybody wants to use multiple layers of paper in their paper-based device. Yager is trying to develop devices that perform multistep reactions using single pieces of paper. “I’m a monopapyrist,” he says. “I’d like all my devices to have one continuous strip of paper, no matter what the shape is.”

The challenge with using only one piece of paper is how to get all the reagents to the right place at the right time. Control of fluid flow is a critical part of that process. In conventional microfluidic devices, pumps control fluid flow. With paper, the fluid naturally wicks through the device. “One of the great things about paper is you get to throw away the pumps,” Yager says. But “the paper material has to be very uniform to do the kinds of things we’re trying to do. We’re trying to program fluid flow rates and arrival times using paper.”

The goal of all that flow control is getting the sample and reagents to a desired spot on a device. “Everything ultimately has to come to the place where I’ll make a measurement,” Yager says. “The whole question is how do I get that spot to change in a pattern and intensity that relates to how much stuff was there.”

Yager and coworkers recently used two-dimensional paper networks to detect a malaria antigen (Anal. Chem., DOI:10.1021/ac300689s). And they are currently working on an isothermal method for nucleic acid amplification on a paper device. To design such devices, they first figure out how to make each individual step work on separate pieces of paper and then connect those “subroutines” on a single piece of paper. “We’ve developed a tool kit of paper processes,” he says.

Many paper devices are laminated, both to hold them together and to keep out contaminants. But lamination can require extra steps to incorporate sample inlets. Andres W. Martinez and coworkers at California Polytechnic State University, San Luis Obispo, have developed a way to use printing instead of lamination to enclose and protect devices (Anal. Chem., DOI:10.1021/ac202837s).

They pattern channels on paper devices using a wax printer, add any reagents needed for the assay, and then run the paper through a standard laser printer. The toner, which is thermally bonded to the paper, encloses and protects the resulting device, making it easier to handle and operate.

Martinez’ experiments suggest that the toner coating is gas permeable, with some water vapor escaping. However, liquid water doesn’t permeate barriers consisting of at least four layers of toner. Martinez believes the toner-sealing method’s optimal use will not be more large-scale manufacturing but instead allowing small labs to carry out rapid prototyping of paper-based devices.

Most specialists of paper-based devices are working on medical tests, and initially Charles Henry, a chemistry professor at Colorado State University, was no exception. In collaboration with researchers at Chulalongkorn University, in Bangkok, he developed a paper device for metabolic disease detection that used electrochemical detection instead of the colorimetric methods favored by most people. Now Henry is instead developing paper-based exposure monitors for occupational health applications.

Among the devices his group has designed are paper-based systems that measure oxidative stress caused by atmospheric aerosols. During this summer’s Colorado wildfires, firefighters wore such paper devices to measure their exposure to oxidative stress from the fires.

His group has also developed paper devices to measure metal particles in occupational settings. The researchers collect metals on filters, punch out disks from the filters, and put those disks on paper devices where the metals are digested with acid and transported to detection reservoirs by the addition of water. The reservoirs contain reagents needed for the colorimetric detection of various metals.

Detection sensitivity has been a challenge, Henry says. In early experiments, an iron-phenanthroline complex formed in the test would develop a ring around the outer edge of the detection reservoir. “We always saw the same color,” Henry says, making it impossible to distinguish different amounts of metal particles. He and his coworkers have dealt with such problems by modifying the paper to make the tests more discriminating.

The number of potential applications of paper-based devices is growing. “I think of this as the next frontier of microfluidics,” Henry says. “When people started off in microfluidics, they said, ‘Here are 10 things you can do with it.’ Those 10 things became 100, and it really grew from there. The same thing is true of paper devices. More and more people are going to see unique applications. The field will continue to grow until it fills underserved niches as an analytical tool or a medical tool.” 

 

Chemical & Engineering News

ISSN 0009-2347

Copyright © 2012 American Chemical Society

Point-of-Care Diagnostics for the Developed and Developing World #paper microfluidics

In this video, Paul Yager, Professor of Bioengineering, University of Washington talks about the paper based diagnostic devices for different types of assays. These devices are cheap, easy to fabricate, don't require instrumentation, very useful in developing world. 

Simple Blood Typing in Paper device

For anyone who has ever wondered what their blood type is, a new paper-based device will literally write the answer, providing an inexpensive and unambiguous way to determine blood type (Angew. Chem. Int. Ed., DOI:10.1002/anie.201201822).

The presence or absence of certain antigens on red blood cells determines a person’s blood type. Specific antibodies will react with these antigens and make the red blood cells clump. Researchers led by Wei Shen, of Australia’s Monash University, use an ink-jet printer to apply these antibodies in the shapes of letters A, B, and X as well as a vertical line onto postage-stamp-sized pieces of paper towel. O and rhesus-negative blood types don’t have antigens that react with these antibodies, so the researchers preprint an O in the same spot as the X and a horizontal line intersecting the vertical line on the paper in red waterproof ink.

Place a few drops of blood on the paper, wash it with saline, and in under a minute,the blood type appears in text. For example, if the blood type is A-positive, antigens will react with printed A antibody to produce a clump of red blood cells in the shape of the letter A and with antibody in the vertical line to form a + sign. The antigens will also cause a red X to form over the preprinted O. For O-negative blood, no reaction with the antibodies would occur, and the preprinted paper would simply read O above a – sign.

Shen got the idea after seeing the film adaptation of J. K. Rowling’s book “Harry Potter and the Chamber of Secrets,” in which the characters query a diary that responds in writing. Shen realized technology he had previously helped develop could be modified to respond in writing to the question: What’s my blood type?

“The ability to form letters that directly report blood type makes it possible for nonexperts to interpret the results rapidly, which is of particular importance in rapid-response scenarios,” comments John D. Brennan, an expert in bioanalytical chemistry at McMaster University in Ontario. “This method also shows the advantage of implementing simple ink-jet printers to produce paper assays rather than conventional lateral flow printers, which produce only lines.”

 

Chemical & Engineering News

ISSN 0009-2347

Copyright © 2012 American Chemical Society

http://cen.acs.org/articles/90/i18/Blood-Typing-Made-Simple.html

Laminar Flow in Paper Microfluidics

These days I am more into paper microfluidics. I am hoping to work on these devices in future. These devices will have more values in developing countries which lack resources. Here, I post a video from youtube. The video shows a controlled flow of reagent in 2D paper networks.