The floating gate, electrolyte-gated transistor (FGT) is a chemical sensing device utilizing a floating gate electrode to physically separate and electronically couple the active sensing area with the transistor. The FGT platform has yielded promising results for the detection of DNA and proteins, but questions remain regarding its fundamental operating mechanism. Using carboxylic acid-terminated self-assembled monolayers (SAMs) exposed to solutions of different pH, we create a charged surface and hence characterize the role that interfacial charge concentration plays relative to capacitance changes. The results agree with theoretical predictions from conventional double-layer theory, rationalizing nonlinear responses obtained at high analyte concentrations in previous work using the FGT architecture. Our study elucidates an important effect in the sensing mechanism of FGTs, expanding opportunities for the rational optimization of these devices for chemical and biochemical detection.

Printed electrolyte-gated transistors (EGTs) are an emerging biosensor platform that leverage the facile fabrication engendered by printed electronics with the low voltage operation enabled by ion gel dielectrics. The resulting label-free, nonoptical sensors have high gain and provide sensing operations that can be challenging for conventional chemical field effect transistor architectures. After providing an overview of EGT device fabrication and operation, we highlight opportunities for microfluidic enhancement of EGT sensor performance via multiplexing, sample preconcentration, and improved transport to the sensor surface.

The electrolyte gated transistor with a floating gate (FGT) is a promising sensing platform for both chemical and biodetection applications due to its fast, label-free response, low voltage operation, and simple fabrication by printing and conventional lithography. We present here a unified framework for understanding how FGTs measure changes in interfacial capacitance and surface charge, using selfassembled monolayers (SAMs) on the FGT detection area as model systems. The capacitance measurements take advantage of alkyl thiol SAMs with different chain lengths, while the charge experiments deprotonate 11-mercaptoundecanoic acid by changing solution pH. The effects of capacitance and surface charge are identified readily by analysis of the changes in the quasi-static current-voltage (I D -V G ) characteristics of a stand-alone FGT in response to changes in the surface properties; changes in capacitance produce changes in slope, whereas changes in surface charge cause horizontal shifts in the transfer curves. For sensing applications, it is preferable to integrate the FGT into a resistor-loaded inverter to take advantage of the amplified voltage output relative to a standalone FGT. For inverters, changes in capacitance lead to changes in inverter gain, whereas changes in surface charge produce horizontal shifts in the inverter curves. A capacitance sensitivity of 70 mV/(μF/cm 2 ) and a charge sensitivity of 40 mV/(μC/cm 2 ) are obtained from the inverter output voltages. The ability to sense both capacitance and charge, and to distinguish between them, makes FGTs attractive for the detection of a wide variety of targets in chemical and biological sensing applications.

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Background: In 2017, over half the global burden of typhoid fever was projected to have occurred in India. In the absence of contemporary population-based data, it is unclear whether declining trends of hospitalization for typhoid in India reflect increased antibiotic treatment or a true reduction in infection. Methods: We conducted weekly surveillance for acute febrile illness and measured the incidence of blood culture-confirmed typhoid fever in a prospective cohort of children 6 months to 14 years old at three urban and one rural site in India between 2017 and 2020. At an additional urban and five rural sites, we combined blood culture testing of hospitalized patients with fever with health care utilization surveys to estimate incidence in the community. Results: 24,062 children were enrolled across four cohorts, contributing 46,959 child years of observation (CYO). 299 culture-confirmed typhoid cases were recorded, with incidence per 100,000 CYO of between 576 and 1173 in urban sites, and 35 in rural Pune. The estimated incidence of typhoid fever from hospital surveillance ranged between 12 and 1622 per 100,000 CYO in children 6 months to 15 years, and between 108 and 970 per 100,000 person-years among those above 15 years, although there was more uncertainty in these estimates. S . paratyphi was isolated from 33 children, overall incidence of 68 per 100,000 CYO after adjusting for age Conclusions: The incidence of typhoid fever in urban India remains high.