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Nanomaterial-based field-effect transistors (FETs) have been proposed for real-time, label-free detection of various biological species. However, two major challenges have limited their use in physiological samples: screening of the analyte charge by electrolyte ions (Debye screening) and non-specific adsorption. Here, these challenges are overcome by combining highly stable FETs based on single-walled semiconducting carbon nanotube (SWCNTs) networks with a novel surface functionalization comprising: 1) short nanobody (VHH) receptors, and 2) a polyethylene glycol (PEG) layer. Nanobodies are stable, easy-to-produce biological receptors that are very small (∼2–4 nm), thus enabling analyte binding closer to the sensor surface. Despite their unique properties, nanobodies have not been used yet as receptors in FET based biosensors. The addition of PEG strongly enhances the signal in high ionic strength environment. Using green fluorescent protein (GFP) as a model antigen, high selectivity and sub-picomolar detection limit with a dynamic range exceeding 5 orders of magnitude is demonstrated in physiological solutions. In addition, long-term stability measurements reveal a low drift of SWCNTs of 0.05 mV/h. The presented immunoassay is fast, label-free, does not require any sample pretreatment or washing steps. [ABSTRACT FROM AUTHOR]

Nanomaterial-based field-effect transistors (FETs) have been proposed for real-time, label-free detection of various biological species. However, screening of the analyte charge by electrolyte ions (Debye screening) has so far limited their use in physiological samples. Here, this challenge is overcome by combining FETs based on single-walled semiconducting carbon nanotube networks (SWCNTs) with a novel surface functionalization comprising: (1) short nanobody receptors, and (2) a polyethylene glycol layer (PEG). Nanobodies are stable, easy-to-produce, short biological receptors (~2–4 nm) that enable analyte binding closer to the sensor surface. The addition of PEG enhances the signal in high ionic strength environment. Using green fluorescent protein (GFP) as a model antigen, high selectivity and sub-picomolar detection limit with a dynamic range exceeding 4 orders of magnitude is demonstrated in physiological solutions. The presented immunoassay is fast, label-free, does not require any sample pre-treatment or washing steps.

A novel, cheap, disposable and single-use nanoparticles-based nanochannel platform assembled on a flexible substrate for label-free immunosensing is presented. This sensing platform is formed by the dip-coating of a homogeneous and assembled monolayer of carboxylated polystyrene nanospheres (PS, 200 and 500 nm-sized) onto the working area of flexible screen-printed indium tin oxide/polyethylene terephthalate (ITO/PET) electrodes. The spaces between the self-assembled nanospheres generate well-ordered nanochannels, with inter-PS particles distances of around 65 and 24 nm respectively. The formed nanochannels are used for the effective immobilization of antibodies and subsequent protein detection based on the monitoring of [Fe(CN)] flow through diffusion and the decrease in the differential pulse voltammetric signal upon immunocomplex formation. The obtained sensing system is nanochannel-size dependent and allows human immunoglobulin G (IgG) (chosen as a model analyte) to be detected at levels of 580 ng/mL. The system also exhibits an excellent specificity against other proteins present in real samples and shows good performance with a human urine sample. The developed device represents an integrated and simple biodetection system which overcomes many of the limitations of previously reported nanochannels-based approaches and can be extended in the future to several other immuno and DNA detection systems. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Silica-based electrochemical immunosensors recently gained much importance for detecting antigens and biomarkers responsible for cancer diagnosis. This review describes fabrication and chemical modification of the surfaces of mesoporous silica materials for biomedical and immunosensing applications. We also present a comprehensive overview of current developments and key issues in the determination of some biological molecules with particular emphasis on evaluating the models. [Copyright &y& Elsevier]