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?

ELISA with 100 fold improvement in detection limit & 100 fold less sample volume

My first paper on microfluidic work has been published in Analitica Chimica Acta. This was the first project I worked on for my PhD work (actually the very first one didn't work. That was my advisor's crazy idea he wanted me to give a try.  We abandoned that later on). 

In this article, we have demonstrated a novel approach to enhancing the sensitivity of enzyme-linked immunosorbent assays (ELISA) through pre-concentration of the enzyme reaction product (resorufin/4- methylumbelliferone) in free solution. 

Highly sensitive analytical techniques are required to estimate small amounts of disease markers (e.g., antibodies/antigens) in bodily fluids in order to detect the onset of dangerous diseases like cancers at their early stages. Here is the abstract of this paper. 

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.