Electronic Detection of Biomarkers by Si Field-Effect Transistor from Undiluted Sample Solutions with High Ionic Strengths

Abstract

In this study, we have developed a new detection method using Si field effect transistor (FET)-type biosensors, which enables the direct monitoring of antigen-antibody binding within very high-ionic-strength solutions such as 1×PBS and human serum. In the new method, as no additional dilution or desalting processes are required, the FET-type biosensors can be more suitable for ultrasensitive and real-time analysis of raw sample solutions. The new detection scheme is based on the observation that the strength of antigen-antibody-specific binding is significantly influenced by the ionic strength of the reaction solutions. For a prostate specific antigen (PSA), in some conditions, the binding reaction between PSA and anti-PSA in a low-ionic strength reaction solution such as 10 µM phosphate buffer is weak (reversible), while that in high-ionic strength reaction solutions such as 1×PBS or human serum is strong.Key Words: Electronic detection, PSA, Si field effect transistor (FET), Ionic strength, Real-timeStep 1 (G1 measurement)Step 2 (reaction)Step 3

A comparison between oestradiol aptamers as receptors in CNT FET biosensors

“…While this would suggest that 1 × PBS is the preferable sensing environment, the increased ionic screening caused by higher ionic strengths is well known to result in a reduced signal in FET biosensors. 38,39 This dilemma can potentially be addressed through the use of sensing methods or sensor modifications that mitigate the effect of ionic screening, 39–41 however it is also possible to create aptamers that produce sensing signals in high ionic strength solutions without unusual modifications to the sensor or sensing protocol. 42,43 Producing aptamers using the capture-SELEX method, which selects for structure switching aptamers, would benefit sensor applications.…”

Label‐Free Sensing of Biomolecules with Field‐Effect Devices for Clinical Applications

“…Notably, in order to reduce the ionic strength of the solution, the serum samples were desalted in a rapid and simple purification step. An ultrasensitive, label‐free and real‐time PSA biosensor (with detection limit of 1 fg/mL or 30 aM in human serum without any pretreatment) was developed in 109, 110 using top‐down‐fabricated n‐type SiNW‐FETs. To obtain a thin conducting channel with high sensitivity to biomolecules, the top Si layer with 100 nm thickness was thinned down to 40 nm by wet‐thinning process.…”