We report a fully integrated SERS-based microdroplet platform for simultaneous detection of various concentrations of a reagent.

A surface-enhanced Raman scattering-based lateral flow assay (SERS-LFA) technique has been developed for the rapid and accurate diagnosis of scrub typhus. Lateral flow kits for the detection of O. tsutsugamushi IgG (scrub typhus biomarker) were fabricated, and the calibration curve for various standard clinical sera concentrations were obtained by Raman measurements. The clinical sera titer values were determined by fitting the Raman data to the calibration curve. To assess the clinical feasibility of the proposed method, SERS-LFA assays were performed on 40 clinical samples. The results showed good agreement with those of the standard indirect immunofluorescence assay (IFA) method. SERS-LFA has many advantages over IFA including the less sample volume, simpler assay steps, shorter assay time, more systematic quantitative analysis, and longer assay lifetime. As SERS strips can be easily integrated with a miniaturized Raman spectrophotometer, field serodiagnosis is also more feasible.

No abstract

No abstract

No abstract

In this study, we developed a high-performance extended-gate ion-sensitive field-effect transistor (EG-ISFET) sensor on a flexible polyethylene naphthalate (PEN) substrate. The EG-ISFET sensor comprises a tin dioxide (SnO 2) extended gate, which acts as a detector, and an amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) for a transducer. In order to self-amplify the sensitivity of the pH sensors, we designed a uniquely-structured a-IGZO TFT transducer with a high-k engineered top gate insulator consisting of a silicon dioxide/tantalum pentoxide (SiO 2 /Ta 2 O 5) stack, a floating layer under the channel, and a control gate coplanar with the channel. The SiO 2 /Ta 2 O 5 stacked top gate insulator and inplane control gate significantly contribute to capacitive coupling, enabling the amplification of sensitivity to be enlarged compared to conventional dual-gate transducers. For a pH sensing method suitable for EG-ISFET sensors, we propose an in-plane control gate (IG) sensing mode, instead of conventional single-gate (SG) or dual-gate (DG) sensing modes. As a result, a pH sensitivity of 2364 mV/pH was achieved at room temperature-this is significantly superior to the Nernstian limit (59.15 mV/pH at room temperature). In addition, we found that non-ideal behavior was improved in hysteresis and drift measurements. Therefore, the proposed transparent EGISFFET sensor with an IG sensing mode is expected to become a promising platform for flexible and wearable biosensing applications.

The sensitivity of conventional ion-sensitive field-effect transistors (ISFETs) is limited by the Nernst equation, which is not sufficient for detecting weak biological signals. In this study, we propose a silicon-on-insulator-based coplanar dual-gate (Cop-DG) ISFET pH sensor, which exhibits better performance than the conventional ISFET pH sensor. The Cop-DG ISFETs employ a Cop-DG consisting of a control gate (CG) and a sensing gate (SG) with a common gate oxide and an electrically isolated floating gate (FG). As CG and SG are capacitively coupled to FG, both these gates can efficiently modulate the conductance of the FET channel. The advantage of the proposed sensor is its ability to amplify the sensitivity effectively according to the capacitive coupling ratio between FG and coplanar gates (SG and CG), which is determined by the area of SG and CG. We obtained the pH sensitivity of 304.12 mV/pH, which is significantly larger than that of the conventional ISFET sensor (59.15 mV/pH, at 25 °C). In addition, we measured the hysteresis and drift effects to ensure the stability and reliability of the sensor. Owing to its simple structure, cost-effectiveness, and excellent sensitivity and reliability, we believe that the Cop-DG ISFET sensor provides a promising point-of-care biomedical applications.

In this paper, we fabricated an AlGaN/GaN high electron mobility transistor (HEMT) pH sensor with an extended-gate (EG). As the carrier mobility of the transducer that is used as the biosensor is increased, the electrical signal conversion efficiency of the biomaterials is improved. Therefore, the HEMT is a more suitable transducer platform than the conventional silicon-based transistor. The fabricated AlGaN/GaN device showed an electron density of 9.0 × 1012 cm-2, and an electron mobility of 1,990 cm2/V-s. In order to reduce the gate leakage current, which is a drawback of conventional HEMT devices, we deposited a 3-nm thick Al2O3 layer as a top-gate oxide by the atomic layer deposition (ALD) method; the fabricated HEMT has a metal–insulator semiconductor (MIS) structure. In addition, we used the EG to implement the disposable biosensor. Although the EG (a sensing membrane) is contaminated and destroyed, the HEMT (a transducer) can be reused. We evaluated the pH sensing characteristics using a pH sensor, which was implemented by connecting the HEMT and EG. The EG HEMT pH sensor showed a sensitivity of 57.6 mV/pH, which is close to the Nernst limit (approximately 59 mV/pH), and a linearity of 98.93%. To verify the stability and reliability of the implemented EG HEMT pH sensor, we measured the real-time response. The EG HEMT pH sensor has an error of only 2.39% of the signal. Therefore, we expect that the EG-based AlGaN/GaN HEMT pH sensor will be a suitable next-generation biosensor platform for a high electrical signal change efficiency of biomaterials, disposable, and point-of-care systems.