Abstract

Thermoelectric ELISA is a novel method for performing immunoassays in a microfluidic device in which the concentration of the analyte is determined by detecting the heat of the enzymatic reaction between glucose oxidase conjugated to an IgG detection antibody and glucose using a thin-film antimony–bismuth thermopile. The heat transfer in the system is mathematically modeled and the resulting differential equations solved using fundamental numerical methods. The theoretical analysis predicts the output voltage change of a thin-film thermopile positioned adjacent to the reaction zone. The predicted thermopile temperature increase is 0.35 m °C, which occurs 80 s after the substrate reaches the reaction zone. This temperature increase corresponds to a 2.45 μV peak height of the thermopile response and is easily detectable with 8-digit voltammetry electronics. The ELISA method was demonstrated experimentally by antibody-mediated detection of 8-hydroxydeoxyguanosine (8OHdG), an important biomarker of oxidative stress, in mouse urine samples. Experimental results correlate well with results from the mathematical simulations. Additional mathematical simulations were performed to evaluate the effect of flow rate and injection sample volume on the thermopile response. Results indicated that increasing the flow rate and decreasing the substrate injection volume decreased the magnitude and the duration of the thermoelectric response, but also accelerate the time required for sample analysis. The optimization of the flow rate and substrate injection volume is discussed herein.

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