Detection of disease biomarkers from whole blood is very important in disease prevention and management. However, new generation assays like point-of-care or mobile diagnostics face a myriad of challenges in detecting proteins from whole blood. In this research, we have designed, fabricated, and characterized a portable biomedical sensor for the detection of cardiac troponin I (cTnI) directly from whole blood, without sample pretreatments. The sensing methodology is based on an extended gate electrical double layer (EDL) gated field effect transistor (FET) biosensor that can offer very high sensitivity, a wide dynamic range, and high selectivity to target analyte. The sensing methodology is not impeded by electrostatic screening and can be applied to all types of FET sensors. A portable biomedical system is designed to carry out the diagnostic assay in a very simple and rapid manner, that allows the user to screen for target protein from a single drop of blood, in 5 min. This biomedical sensor can be used in hospitals and homes alike, for early detection of cTnI which is a clinical marker for acute myocardial infarction. This sensing methodology could potentially revolutionize the modern health care industry.

Lead ion selective membrane (Pb-ISM) coated AlGaN/GaN high electron mobility transistors (HEMT) was used to demonstrate a whole new methodology for ion-selective FET sensors, which can create ultra-high sensitivity (−36 mV/log [Pb2+]) surpassing the limit of ideal sensitivity (−29.58 mV/log [Pb2+]) in a typical Nernst equation for lead ion. The largely improved sensitivity has tremendously reduced the detection limit (10−10 M) for several orders of magnitude of lead ion concentration compared to typical ion-selective electrode (ISE) (10−7 M). The high sensitivity was obtained by creating a strong filed between the gate electrode and the HEMT channel. Systematical investigation was done by measuring different design of the sensor and gate bias, indicating ultra-high sensitivity and ultra-low detection limit obtained only in sufficiently strong field. Theoretical study in the sensitivity consistently agrees with the experimental finding and predicts the maximum and minimum sensitivity. The detection limit of our sensor is comparable to that of Inductively-Coupled-Plasma Mass Spectrum (ICP-MS), which also has detection limit near 10−10 M.

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Chromium, one of the top five toxic heavy metals ranked according to significance in public health by WHO, exists as Cr(III) which is naturally occurring or Cr(VI) which is anthropogenic in origin. The EPA specifies the maximum contaminant level in drinking water to be 10−6 M or 0.1 mg/L or 100 ppb for the total dissolved Cr. To ensure the water consumed by the population has these pollutants below the safe threshold, this report demonstrates a field effect transistor (FET) based sensor design incorporating a highly target specific ion-selective membrane combined with extended gate technology which manifests sensitivity exceeding the Nernst limit aided by the high field effect in the short gap region of extended gate technology. Characterization and repeated testing of the portable device revealed a commendable calibration sensitivity of 99 mV/log [Cr3+] and 71 mV/log [Cr6+] for Cr(III) and Cr(VI) respectively, well surpassing the Nernst limits of sensitivity and offering a detection limit lower than ion-selective electrodes (10−6 M), and comparable to the expensive benchtop laboratory instrument, ICP-MS. This report presents a robust, easy to fabricate, economic and efficient handheld biosensor to detect the chromium in a liquid sample whether it exists as Cr(III) or Cr(VI).

Exposure to heavy metal ions poses grave danger to public health and reliable and affordable water quality monitoring system that can rapidly screen for heavy metal ion contamination is necessary. In this research, we have developed a unique sensing methodology to detect heavy metal ions such as Pb 2+ and Hg 2+ in water sources, using ion-selective high electron mobility transistor sensor (ISHEMT). A detailed investigation of the sensing and selectivity characteristics of ISHEMT is carried out and a theoretical model is proposed for the illustration of the enhanced sensitivity and selectivity. The high field modulated ISHEMT sensor displays very high sensitivity, much beyond the ideal Nernstian slope, offering very low detection limit (10 −10 M for Pb 2+ and 10 −11 M for Hg 2+ ). The sensing characteristics are not affected by the presence of interfering ions and the selective sensor response has been validated using fixed interference and separate solution methods. These sensor characteristics are superior than the traditional ISE or ISFET sensors, and at par with laboratory standard technologies like ICP-MS. The miniaturized, inexpensive and user-friendly sensor technology can provide consumers with an affordable and convenient means of securing safe and contamination free water and food consumption.

Mercury ion selective membrane (Hg-ISM) coated extended gate Field Effect transistors (ISM-FET) were used to manifest a novel methodology for ion-selective sensors based on FET’s, creating ultra-high sensitivity (−36 mV/log [Hg2+]) and outweighing ideal Nernst sensitivity limit (−29.58 mV/log [Hg2+]) for mercury ion. This highly enhanced sensitivity compared with the ion-selective electrode (ISE) (10−7 M) has reduced the limit of detection (10−13 M) of Hg2+ concentration’s magnitude to considerable orders irrespective of the pH of the test solution. Systematical investigation was carried out by modulating sensor design and bias voltage, revealing that higher sensitivity and a lower detection limit can be attained in an adequately stronger electric field. Our sensor has a limit of detection of 10−13 M which is two orders lower than Inductively Coupled Plasma Mass Spectrometry (ICP-MS), having a limit of detection of 10−11 M. The sensitivity and detection limit do not have axiomatic changes under the presence of high concentrations of interfering ions. The technology offers economic and consumer friendly water quality monitoring options intended for homes, offices and industries.

This study reports the development of a rapid heavy metal ion screening tool for whole blood samples. The test system consists of an ion selective membrane-based impedance modulated field effect transistor (FET) sensor and a portable sensor measurement unit. This study focuses on the direct detection of lead ions in whole blood, without extensive sample pre-treatments. The sensing methodology is based on impedance changes in the membrane due to the specific ionophore-target metal ion interaction in the presence of a strong electric field. The changes in impedance caused by heavy metal ions are amplified by the FET to obtain a highly sensitive lead ion detection, with very low detection limit (near 10−11 ∼ 10−10 M Pb2+). To reduce the complexity and enhance sensor performance, the whole blood samples are fractionated on chip without any external actuation/automation using simple gravitational blood cell separation. The test results in PBS, human serum and whole blood samples demonstrate high sensitivity and wide dynamic range of lead ion detection. The miniaturized extended gate FET sensor system is ideal for point of care and home-care diagnostics for heavy metal ion in blood.