The highly sensitive detection of peanut allergens (PAs) using silicon-based electrolyte-gated transistors (Si-EGTs) was demonstrated. The Si-EGT was made using a top-down technique. The fabricated Si-EGT showed excellent intrinsic electrical characteristics, including a low threshold voltage of 0.7 V, low subthreshold swing of <70 mV/dec, and low gate leakage of <10 pA. Surface functionalization and immobilization of antibodies were performed for the selective detection of PAs. The voltage-related sensitivity (SV) showed a constant behavior from the subthreshold regime to the linear regime. The current-related sensitivity (SI) was high in the subthreshold regime and then significantly decreased as the drain current increased. The limit of detection (LOD) was calculated to be as low as 25 pg/mL based on SI characteristics, which is the lowest value reported to date in the literature for various sensor methodologies. The Si-EGT showed selective detection of PA through a non-specific control test. These results confirm that Si-EGT is a high-sensitivity and low-power biosensor for PA detection.
The recent Coronavirus Disease 2019 (COVID‐19) outbreak strongly propels advancements in biosensor technology, leading to the emergence of novel methods for virus detection. Among them, those using nanostructured field‐effect transistors (FETs) provide an ultrasensitive approach toward point‐of‐care diagnostics. However, the application of these biosensors in analyzing biofluids has been limited by their reduced screening length in high ionic strength liquids. To address this challenge, a solution is presented involving the surface modification of FETs with a hydrogel based on star‐shaped polyethylene glycol. This hydrogel is loaded with specific antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) spike protein. By incorporating the hydrogel, the effective Debye length is effectively increased, thereby preserving the sensitivity in biofluids. The efficacy of this approach is demonstrated by employing silicon nanonet‐based FETs for the detection of viral antigens in both buffer and saliva, as well as cultured viral particle dispersions. Moreover, positive and negative patient samples are successfully differentiated, showcasing the practical application of this method. Finally, a theoretical frame is proposed to elucidate the underlying mechanism behind the preservation of sensitivity.
The recent COVID-19 outbreak has strongly pushed the field of biosensors, resulting in multiple new approaches for quantitative virus detection. Among them, those using nanostructured field-effect transistors (FETs) as transducers provide an ultrasensitive approach requiring simple setups for their miniaturization toward point-of-care diagnostics of the disease. However, this type of biosensors suffer from limited sensitivity when it comes to analyzing biofluids due to their shortened screening length in presence of complex liquids with high ionic strength. In this work we propose a solution to this problem, which consists on the surface modification of the FETs with a hydrogel based on star-shaped polyethylene glycol and loaded with specific antibodies against SARS-CoV-2 spike protein. The hydrogel increases the effective Debye length, allowing to preserve the sensitivity in high ionic strength solutions. We provide the demonstration employing silicon nanonet-based FETs for the detection of viral antigens in buffer and in saliva, as well as cultured viral particles. We finally discriminate positive and negative patient samples (nasopharyngeal swab), and propose the theoretical frame that discusses the mechanism of the sensitivity preservation based on the presence of the pegylated hydrogel.
The SARS-CoV-2 pandemic has increased the demand for low-cost, portable and rapid biosensors, driving huge research efforts toward new nanomaterial-based approaches with high sensitivity. Many of them employ antibodies as bioreceptors, which have a costly development process requiring animal facilities. Recently, sybodies emerged as an alternative new class of synthetic binders/receptors with high antigen binding efficiency, improved chemical stability, and lower production costs via animal-free methods. Their smaller size is an important asset to consider in combination with ultrasensitive field-effect transistors (FETs) as transducers, which respond more intensely when the biorecognition occurs in close proximity to their surface. This work demonstrates the immobilization of sybodies against the spike protein of the virus on silicon surfaces, which are often the integral part of the semiconducting channel of FETs. Immobilized sybodies maintain the capability to capture antigens even at low concentrations in the femtomolar range, as observed by fluorescence microscopy. Finally, the first proof-of-concept of sybody-modified FET sensing is provided, using a nanoscopic silicon net as the sensitive area where the sybodies are immobilized. The future development of further sybodies against other biomarkers and their generalization in biosensors could be critical to decrease the cost of biodetection platforms in future pandemics.
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