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.

Analyte preconcentration results in detecting lower concentrations of cancer marker

It is important to detect lower concentrations of disease (like various cancers) markers in human bodily fluids reliably. The ability to detect lower analyte concentration would allow us to identify the onset of diseases in their early stages and start treatment process.

In an effort to make a device that could measure lower concentrations of protein, researchers of Dutta  group at the University of Wyoming have developed a microfluidic device in which the analyte protein molecules are preconcentrated infront of membrane inside the channel. Enzyme Linked Immunosorbent Assay (ELISA) was performed on the same channel and the signal generated from the enzyme reaction was increased by a factor of 200.

In their current work reported, they have shown a reduction in the smallest detectable concentration of the tumor marker CA 199-9 and Blue tongue Viral antibody by over 2 orders of magnitude compared to immunoassays without preconcentration. This led to the improvement in the lowest analyte concentration detectable (LOD) by a factor of 20. Their device only required ~5 uL analyte and other solutions to complete the assay in contrast to conventional microtiter plate based assayed (~100uL).

There are several methods to amplify the ELISA signal and some of them involve preconcentration of enzyme reaction product (e.g resorufin) molecules. Dutta groups new method is unique in terms of preconcentrating target analyte-proteins. They used photopolymerized semipermeable membrane fabricated inside bonded glass microchip for preconcentrating analytes.

Details of this work has been published recently in Analytical Chemistry journal.