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Chemical Analog-to-Digital Signal Conversion Based on Robust Threshold Chemistry and Its Evaluation in the Context of Microfluidics-Based Quantitative Assays

Huynh, Toan and Sun, Bing and Li, Liang and Nichols, Kevin P. and Koyner, Jay L. and Ismagilov, Rustem F. (2013) Chemical Analog-to-Digital Signal Conversion Based on Robust Threshold Chemistry and Its Evaluation in the Context of Microfluidics-Based Quantitative Assays. Journal of the American Chemical Society, 135 (39). pp. 14775-14783. ISSN 0002-7863. PMCID PMC3860884. doi:10.1021/ja4062882.

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In this article, we describe a nonlinear threshold chemistry based on enzymatic inhibition and demonstrate how it can be coupled with microfluidics to convert a chemical concentration (analog input) into patterns of ON or OFF reaction outcomes (chemical digital readout). Quantification of small changes in concentration is needed in a number of assays, such as that for cystatin C, where a 1.5-fold increase in concentration may indicate the presence of acute kidney injury or progression of chronic kidney disease. We developed an analog-to-digital chemical signal conversion that gives visual readout and applied it to an assay for cystatin C as a model target. The threshold chemistry is based on enzymatic inhibition and gives sharper responses with tighter inhibition. The chemistry described here uses acetylcholinesterase (AChE) and produces an unambiguous color change when the input is above a predetermined threshold concentration. An input gives a pattern of ON/OFF responses when subjected to a monotonic sequence of threshold concentrations, revealing the input concentration at the point of transition from OFF to ON outcomes. We demonstrated that this threshold chemistry can detect a 1.30-fold increase in concentration at 22 °C and that it is robust to experimental fluctuations: it provided the same output despite changes in temperature (22–34 °C) and readout time (10-fold range). We applied this threshold chemistry to diagnostics by coupling it with a traditional sandwich immunoassay for serum cystatin C. Because one quantitative measurement comprises several assays, each with its own threshold concentration, we used a microfluidic SlipChip device to process 12 assays in parallel, detecting a 1.5-fold increase (from 0.64 (49 nM) to 0.96 mg/L (74 nM)) of cystatin C in serum. We also demonstrated applicability to analysis of patient serum samples and the ability to image results using a cell phone camera. This work indicates that combining developments in nonlinear chemistries with microfluidics may lead to development of user-friendly diagnostic assays with simple readouts.

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URLURL TypeDescription Information CentralArticle
Ismagilov, Rustem F.0000-0002-3680-4399
Additional Information:© 2013 American Chemical Society. Published In Issue: October 02, 2013. Article ASAP: September 24, 2013. Received: June 24, 2013. This work was supported in part by the NIH Director’s Pioneer Award DP10D003584, NIH Career Development Award K23DK081616 (J.K.), DARPA Cooperative Agreement No. HR0011-11-2-0006, and ONR Grant No. N00014-08-1-0936. The authors thank Jordany Maignan and Roman Manetsch for providing pure syn-(S)-TZ2PIQ-A5 (AChE inhibitor), Elena K. Davydova and Jason E. Kreutz for aiding in selection of cystatin C, Liang Ma for the idea of depositing plugs, Weishan Liu for advice about manipulation of magnetic beads, Andrew Chiang for references about thresholds, Yu-Hsiang Hsu for suggestions for the imaging of chips, Stefano Begolo for suggestions about image processing, and Bridget Samuels and Whitney Robles for contributions to the writing and editing of this manuscript.
Funding AgencyGrant Number
Defense Advanced Research Projects Agency (DARPA)HR0011-11-2-0006
Office of Naval Research (ONR)N00014-08-1-0936
Issue or Number:39
PubMed Central ID:PMC3860884
Record Number:CaltechAUTHORS:20131024-155658108
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42058
Deposited By: Whitney Robles
Deposited On:24 Oct 2013 23:48
Last Modified:10 Nov 2021 04:37

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