Abstract
Detecting proteins at low concentrations in high-ionic-strength conditions by silicon nanowire field-effect transistors (SiNWFETs) is severely hindered due to the weakened signal, primarily caused by screening effects. In this study, aptamer as a signal amplifier, which has already been reported by our group, is integrated into SiNWFET immunosensors employing antigen-binding fragments (Fab) as the receptors to improve its detection limit for the first time. The Fab-SiNWFET immunosensors were developed by immobilizing Fab onto Si surfaces modified with either 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde (GA) (Fab/APTES-SiNWFETs), or mixed self-assembled monolayers (mSAMs) of polyethylene glycol (PEG) and GA (Fab/PEG-SiNWFETs), to detect the rabbit IgG at different concentrations in a high-ionic-strength environment (150 mM Bis-Tris Propane) followed by incubation with R18, an aptamer which can specifically target rabbit IgG, for signal enhancement. Empirical results revealed that the signal produced by the sensors with Fab probes was greatly enhanced compared to the ones with whole antibody (Wab) after detecting similar concentrations of rabbit IgG. The Fab/PEG-SiNWFET immunosensors exhibited an especially improved limit of detection to determine the IgG level down to 1 pg/mL, which has not been achieved by the Wab/PEG-SiNWFET immunosensors.
Highlights
Silicon nanowire field-effect transistor (SiNWFET) biosensors have been demonstrated as ultra-sensitive devices which can provide the real-time and label-free detection of numerous targets [1], especially proteins, by so-called immunosensors [2]
Determining proteins at low concentrations in high-ionic-strength conditions by SiNWFETs is limited by the small Debye length and deteriorated signal
A method for this problem integrating aptamer as signal amplifier into SiNWFET immunosensors and employing Fab as bio-receptor is presented for the first time
Summary
Silicon nanowire field-effect transistor (SiNWFET) biosensors have been demonstrated as ultra-sensitive devices which can provide the real-time and label-free detection of numerous targets [1], especially proteins, by so-called immunosensors [2]. R18, an RNA aptamer which can bind with rabbit IgG [30], is employed as the amplifier to stabilize and enhance the signal produced from protein detections in high-ionic-strength conditions for the as-designed sensors. Assembling SiNWFET, Fab, mixedSAM, and aptamer can release a novel generation of ultrasensitive FET-based biosensors, overcoming the limitations of Debye length and interference from high-ionic-strength environments. Sensors 2021, 21, 650 tion effect of integrating both Fab and aptamer into the SiNWFET immunosensors were from the compact structure of the Fab
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