3-D Diagnosis

Blood test made easy with paper and adhesive tapes

TESTING of blood for iron, glucose and protein levels is a time-consuming and costly affair requiring a series of chemical tests in a laboratory. Researchers from the Harvard University in US invented a device called the 3D µPAD that could do away with the requirement of a laboratory analysis.

The device is portable and can be used to test various constituents of blood simultaneously. Even urine samples can be analyzed this way.

The researchers arranged vertical stacks of patterned paper with alternating water impermeable double-sided adhesive tapes. The arrangement was such that between each two layers of paper there was a layer of adhesive tape creating a three-dimensional network of paper-tape-paper and so on.

The topmost layer of paper had inlets for collecting fluid samples of blood or urine. The inlets led to corresponding openings in the layer of adhesive tape below it. The subsequent layer of paper had channels etched into it which distributed fluids from each inlet into further channels. These channels ended in a complex array of detection spots in the lowest stack of paper. Each layer of tape had openings to allow for flow of fluids without letting them mix.

"Imagine a tank with four channels leading out of it, and each channel then breaks up into four smaller channels, and each smaller channel leads to a smaller tank. When you add fluid to the first tank, it will be distributed through the network of channels into the 16 smaller tanks. We are doing something similar, but on a microscale, and all on paper," explained Andrez Martinez, one of the researchers who contributed to the technology that was published in the December 16 issue of the Journal Proceedings of the National Academy of Sciences.

In this case, the network of channels drew each fluid by capillary action from its inlet at the top, distributing it into the corresponding detection spots below. The inlets, the detection spots and the channels connecting them were etched by impregnating the paper with photoresist (a light sensitive polymer).

Constituent-specific reagents at the detection spots reacted with the constituents of each fluid simultaneously. The device had a control sample as one of the fluids. This helped in analyzing the concentration of each constituent by comparing its colour (after reaction with its reagent) with the colour of that of the control sample. Hence detection of difference in concentrations was easy.

This technology can make up for detection in places where the doctor can't reach on time. Depending on the number of inlets, one device can test blood or urine samples of the entire family. The more the number of detection spots (which can be increased by increasing the stacks of paper), the more the number of constituents to be tested.

One-dimensional paper-based detection devices are used in environmental monitoring, but can test limited number of constituents. In 3D µPADs this limitation can be taken care of by increasing the number of stacks of paper.

Source : Down To Earth, February, 2009