Rapid and Sensitive Pathogen Detection in Serum for Early Sepsis Diagnostics Using an Electrical-Double-Layer Gated Field-Effect Transistor-Based Sensor Array
Authors: Paulose Akhil K , Hou Yueh-Ju , Kalaimani Vishal Mani , Wang Yu-Lin 
Published: September 2023

Sepsis is a major medical inflammatory response to bloodstream infection caused by
pathogens. Over 30 million infections occur due to sepsis in a year throughout the globe.
With over 6 million deaths, sepsis treatment demands timely diagnosis and medical
interventions to prevent large outspread of the infection. Rapid and sensitive detection of
infectious bacteria plays an important role in disease control. However, fast and accurate
diagnosis remains highly challenging for many hospitalized patients. Among various
bacterial diseases, Escherichia coli, (E. coli) a gram-negative bacterium, is the most
frequently and extensively researched and has become a global concern of food safety
problems. Traditional cell culture methods are considered as most accurate method for
bacterial diagnosis. But some microorganisms like Bartonella spp, Treponema pallidum, etc.
are difficult to grow on a culture plate, while some other virus species are unculturable, so
eventually the traditional cell culture may take several days to a week for the diagnostic
results. Hence, over several years, different novel methods have been developed, such as
optical methods, electrochemical methods, molecular detection by PCR etc. Even though
several techniques exist, concerns have been raised regarding their sensitivity, specificity etc.
In addition, various fluorescence-based methods, and Surface Plasmon resonance (SPR)-
based sensors have also been reported for bacterial detection. However, high cost, large
turnaround time, expensive instrumentation, and requirement of skilled personnel are some of
the disadvantages of these existing techniques.
FET biosensors have previously been used in different diagnosis areas. Nowadays, several
FET-based biosensors have been developed, which primarily concentrate on improving the
overall sensitivity of FET devices. However, the charge screening effect observed in a
physiological environment, and additional sample processing increase the complexity of the
sensor platform. To overcome this hurdle, an electrical double layer (EDL) gated FET
biosensor has been proposed and explored in the detection of a variety of biological entities.
Here, we proposed an EDL-FET sensor platform for the detection of Escherichia coli
O157:H7 strain in blood serum. A single-step surface functionalization strategy was used for
immobilizing receptor probes as ssDNA. The probes were designed and immobilized over a
disposable chip containing a pair of gold electrodes. A handheld reader which consists of an
enhancement mode N-channel MOSFETs was connected to the laptop through a USB port to
measure the sensor signals. Pulsed gate voltage was applied to the input electrode and which
modulated the EDL capacitance and potential change eventually resulting in the drain current
of the MOSFET. The probe was immobilized on the gate electrode and tested with different
concentrations of cDNA spiked in TE buffer. The probe-target binding was observed through
fluorescence change and electrically by measuring the change in drain current. In addition,
surface potential change was also examined by performing KPFM test. Similarly, the BioFET
detections were validated for E. coli O157 variants by spiking with short and long DNA
target sequences simultaneously in serum. The test results confirm selectivity by testing
various non-complementary sequences, which ensures the potential of this BioFET as a
point-of-care sensing device.

Figure 1