A platform based on a highly selective and sensitive detection device functionalized with a well-designed artificial biointerface is required for versatile biosensors. We develop a molecularly imprinted polymer (MIP)-coated gate field-effect transistor (FET) biosensor for low-concentration glucose detection in biological fluid samples such as tears in an enzyme-free manner. The MIP includes glucose templates (GluMIP), in which glucose binds to vinylphenylboronic acid in the copolymerized membrane, resulting in the change in the density of molecular charges of the phenylboronic acid (PBA)/glucose complex. The FET biosensor can detect small biomolecules as long as biomolecular recognition events cause intrinsic changes in the density of molecular charges. As a result, the changes in the output voltage detected using the GluMIP-based FET sensor are fitted to the Langmuir adsorption isotherm equation at various concentrations of sugars, showing the low detection limit of 3 μM and the high sensitivity of 115 mV/decade from 100 μM to 4 mM glucose. On the basis of the equation, the stability constant (K a) of PBA with glucose is calculated and found to markedly increase to K a = 1192 M–1, which is higher by a factor of a few hundreds than K a = 4.6 M–1 obtained by nonelectrical detection methods. Moreover, the GluMIP-coated gate FET sensor shows an approximately 200-fold higher selectivity for glucose than for fructose. This is because glucose binds to PBA more selectively than fructose in the templates, resulting in the generation of negative charges. The electrical properties of the MIP-coated electrode are also evaluated by measuring capacitance. Our work suggests a new strategy of designing a platform based on the MIP-coated gate FET biosensor, which is suitable for a highly selective, sensitive, enzyme-free biosensing system.

In this study, we developed an ion-sensitive transparent-gate transistor (IS-TGT) for visible cell sensing. The gate sensing surface of the IS-TGT is transparent in a solution because a transparent amorphous oxide semiconductor composed of amorphous In-Ga-Zn-oxide (a-IGZO) with a thin SiO film gate that includes an indium tin oxide (ITO) film as the source and drain electrodes is utilized. The pH response of the IS-TGT was found to be about 56 mV/pH, indicating approximately Nernstian response. Moreover, the potential signals of the IS-TGT for sodium and potassium ions, which are usually included in biological environments, were evaluated. The optical and electrical properties of the IS-TGT enable cell functions to be monitored simultaneously with microscopic observation and electrical measurement. A platform based on the IS-TGT can be used as a simple and cost-effective plate-cell-sensing system based on thin-film fabrication technology in the research field of life science.

In this paper, we propose a highly sensitive and biocompatible glucose sensor using a semiconductor-based field effect transistor (FET) with a functionalized hydrogel. The principle of the FET device contributes to the easy detection of ionic charges with high sensitivity, and the hydrogel coated on the electrode enables the specific detection of glucose with biocompatibility. The copolymerized hydrogel on the Au gate electrode of the FET device is optimized by controlling the mixture ratio of biocompatible 2-hydroxyethylmethacrylate (HEMA) as the main monomer and vinylphenylboronic acid (VPBA) as a glucose-responsive monomer. The gate surface potential of the hydrogel FETs shifts in the negative direction with increasing glucose concentration from 10 μM to 40 mM, which results from the increase in the negative charges on the basis of the diol-binding of PBA derivatives with glucose molecules in the hydrogel. Moreover, the hydrogel coated on the gate suppresses the signal noise caused by the nonspecific adsorption of proteins such as albumin. The hydrogel FET can serve as a highly sensitive and biocompatible glucose sensor in in vivo or ex vivo applications such as eye contact lenses and sheets adhering to the skin.

No abstract

The COVID-19 pandemic has created urgent demand for rapid detection of the SARS-CoV-2 coronavirus. Herein, we report highly sensitive detection of SARS-CoV-2 nucleocapsid protein (N protein) using nanoparticle-enhanced surface plasmon resonance (SPR) techniques. A crucial plasmonic role in significantly enhancing the limit of detection (LOD) is revealed for exceptionally large gold nanoparticles (AuNPs) with diameters of hundreds of nm. SPR enhanced by these large nanoparticles lowered the LOD of SARS-CoV-2 N protein to 85 fM, resulting in the highest SPR detection sensitivity ever obtained for SARS-CoV-2 N protein.