Search

In this study, a direct and label-free immunosensor was designed and constructed by modifying the screen-printed electrode with graphene nanoplatelets (GNPs) for the detection of the cardiac troponin T (cTnT). Firstly, GNPs were drop-casted onto carbon working electrode. Monoclonal cTnT antibodies were then immobilized on the GNPs via physical adsorption; finally, BSA was introduced to block non-specific binding sites. The detection of cTnT was performed using an electrochemiluminescence (ECL) technique with tris(bipyridine)ruthenium(II) chloride ([Ru(bpy)3]Cl2) used as a luminophore and TPrA (tripropylamine) as a co-reactant. The ECL intensity was demonstrated to be directly proportional to the cTnT concentration where a linear range from 100 pg mL-1 to 5 fg mL-1 of the cTnT detection was established. An extremely low limit of detection was achieved to be 0.05 fg mL-1 with an outstanding specificity. Additionally, this immunosensor showed excellent percentage recovery for real samples analyses in artificially spiked human serum.

In this work, a nanocomposite of gold nanoparticles (AuNPs), carbon nano-onions (CNOs), single-walled carbon nanotubes (SWCNTs) and chitosan (CS) (AuNPs/CNOs/SWCNTs/CS) was prepared for the development of highly sensitive electrochemical immunosensor for the detection of carcinoembryonic antigen (CEA), clinical tumor marker. Firstly, layer-by-layer fabrication of the CEA-immunosensors was studied using cyclic voltammetry (CV) and square wave voltammetry (SWV). By combining the advantages of large surface area and electronic properties of AuNPs, CNOs, SWCNTs, and film forming properties of CS, AuNPs/CNOs/SWCNTs/CS-nanocomposite-modified glassy carbon electrode showed a 200% increase in effective surface area and electronic conductivity. The calibration plot gave a negative linear relationship between log[concentration] of CEA and electrical current with a correlation coefficient of 0.9875. The CEA-immunosensor demonstrated a wide linear detection range of 100 fg mL−1 to 400 ng mL−1 with a low detection limit of 100 fg mL−1. In addition to high sensitivity, reproducibility and large stability, CEA-immunosensor provided an excellent selectivity and resistant-to-interference in the presence of other antigens in serum and hence a potential to be used with real samples.

Recently, there has been a growing concern of consumers on the authenticity of food ingredients including adulteration with porcine and/or its derivatives. Therefore, this work reports on the development of a novel, simple, sensitive and rapid luminol-based electrochemiluminescence (ECL) technique for Sus scrofa (Porcine) DNA detection. Porcine DNA was firstly amplified using loop-mediated isothermal amplification (LAMP) method and subsequently added to luminol solution for further ECL analysis for quantification. The DNA-luminol complexes were formed causing the diffusion of luminol towards the electrode surface to be slowed down and hindered that resulted in low luminol intensity. The LAMP-ECL sensor is shown to be highly specific, sensitive (≥0.1 pg/μL) and rapid (∼5 min for detection). Hence, by employing this principle with carbon screen-printed electrode (SPE), this technique has a potential to be developed further into a compact biosensor for the verifying food authenticity.

Electrochemiluminescence (ECL) technique is defined as luminescence emitted as a result from the occurrence of chemical reaction on the electrode’s surface between luminophore (the light-emitting chemical species) and other species present in the same system when a small potential is applied to the electrode. ECL technique is oftentimes adopted for devising biosensors for the detection of various kinds of proteins by manipulating the interactions between antibody (Ab) and antigen (Ag) – these biosensors are also known as immunosensors. This technique is advantageous for immunosensors as it offers numerous benefits including straightforward operation and low background signal. Furthermore, the performance of these immunosensors can be elevated by integrating carbon nanomaterials (CNMs) into the biosensors and exploiting their excellent electrocatalytic properties for improving the sensitivity and specificity of the biosensors. This chapter comprises of an overview of ECL-based immunosensors integrated with CNMs, accentuating their recent developments and applications.

This study reports a new method of fabrication and application of “green” starch nanoparticles (SNPs) from local sago (Metroxylon Sagu) starch granules employing a high-pressure homogenization procedure. This approach is environmentally friendly, highly feasible, low cost and chemical-free with large-scale production capacity. In this work, SNPs' morphological, particle size and thermal properties were studied. The effects of SNPs concentration (ranging from 0 to 8% w/w) as nano-fillers in composite films’ barrier, transparency and contact angle were also investigated. Our results have shown that the fabricated SNPs exhibited excellent uniformity and spherical shapes. Addition of SNPs have demonstrated to enhance polymeric structure of nanocomposite film due to decreased water vapour permeability and increased contact angle. Sago SNPs as fillers pose an excellent prospect in green composites fabrication for material and biomedical purposes with potential application as carriers for drug delivery.

This study describes a highly sensitive electrochemical immunosensor for the detection of human chorionic gonadotropin (hCG) that uses gold nanoparticles (AuNP) as the electrochemical label and graphene as electrode material. The primary antibody was first immobilized on the graphene working electrode surface by physical adsorption. Antigen hCG was then added and sandwiched with a secondary antibody labelled with AuNPs. After this, a series of sandwich-type immunoreactions were performed on the electrode, AuNPs were quantified by subjecting the immunocomplex to a preoxidation process of high potential at 1.2 V for 40 s and immediately reduced and scanned by differential pulse voltammtery (DPV). Electrodeposition of gold during the reduction stage of the redox reaction was determined by cyclic voltammetry (CV) that showed a linear relationship with the different hCG concentrations. In this study, a linear relationship between reduction peak current signals and hCG concentration from 0 to 500 pg mL−1 (correlation coefficient of 0.97351) with a detection limit of 5 pg mL−1 was obtained.

In this work we exploited the electrostatic interaction of double stranded DNA (dsDNA) with drug components to construct a simple, but highly sensitive, DNA-electrochemical sensor for detecting ciprofloxacin. The following straightforward three-step procedure was performed to determine ciprofloxacin: (i) dsDNA-layer immobilization on the surface of the working graphene-modified screen-printed carbon electrode; (ii) dsDNA-ciprofloxacin interaction for 2 min; and (iii) electrochemical measurement using square-wave voltammetry. An increased oxidation of the guanine component was observed, at +1.0 V, as a result of the electrostatic interaction of positively charged ciprofloxacin with the negatively charged nucleic acid sugar phosphate. Based on the International Conference on Harmonization Guidelines, a linear relationship between the guanine oxidation peak and ciprofloxacin concentration (0.1 to 100 μM) was obtained with a detection limit of 0.1 μM. Our developed sensor is straightforward to construct and use, requiring no multi-step time-consuming preconditioning of electrodes. It is highly sensitive and selective in the detection of ciprofloxacin, and has the potential to be useful in the future fabrication of rapid and portable on-site food safety analysis devices.

A label free electrochemical immunosensor for sensitive detection of porcine serum albumin (PSA) is reported in this work. The immunosensor was constructed by first electrochemically reducing 4-carboxyphenyl diazonium salt, which had been electrochemically generated in situ, to a stable 4-carboxyphenyl layer on carbon nanofiber-modified screen printed electrode. Antibodies were covalently attached onto the electrode using carbodiimide chemistry between the carboxylic groups of the 4-carboxyphenyl layer and amine groups of the antibody. Using the strong affinities of serum albumins towards anions, the increase in cathodic peak current in anionic redox probe after immunocomplex formation with antibodies was used for PSA detection. The reported immunosensor demonstrated a linear range from 0.5 to 500pg/mL for the measurement of PSA with detection limit of 0.5pg/mL in buffer solution. Cross-reactivity studies have shown excellent specificity with satisfactory recovery of PSA in fresh meat samples without the need of sample dilution.

A carbon nanofiber-based label free electrochemical immunosensor for sensitive detection of recombinant bovine somatotropin (rbST) was developed. In this immunosensor design, a mild site-directed antibody immobilization via interaction of boronic acid and oligosaccharide moiety found on Fc region of an antibody was performed to preserve the biological activity of antibody and improve the sensor's sensitivity. Electrochemical characterization of the immunosensor fabrication was carried out by differential pulse voltammetry (DPV) in Fe(CN)6(3-)/Fe(CN)6(4-) probe. A comparison study between different transducer platforms showed carbon nanofiber gave higher current signal response than single-walled carbon nanotube. In this work, calibration curve was obtained from the decrease of DPV peak current of Fe(CN)6(3-)/Fe(CN)6(4-) after immunocomplexed was formed. A linear relationship between DPV current change signal response and rbST concentrations from 1 pg/mL to 10 ng/mL (correlation coefficient of 0.9721) was achieved with detection limit of 1 pg/mL. Our developed immunosensor demonstrated high selectivity in cross-reactivity studies and a good percentage recovery in spiked bovine serum sample.