Nanoplated bismuth titanate sub-microspheres for protein immobilization and their corresponding direct electrochemistry and electrocatalysis

Recent advances in perovskite oxides for non-enzymatic electrochemical sensors: A review

Non-enzymatic electrochemical sensors with significant advantages of high sensitivity, long-term stability, and excellent reproducibility, are one promising technology to solve many challenges, such as the detection of toxic substances and viruses. Among various materials, perovskite oxides have become a promising candidate for use in non-enzymatic electrochemical sensors because of their low cost, flexible structure, and high intrinsic catalytic activity. A comprehensive overview of the recent advances in perovskite oxides for non-enzymatic electrochemical sensors is provided, which includes the synthesis methods of nanostructured perovskites and the electrocatalytic mechanisms of perovskite catalysts. The better sensing performance of perovskite oxides is mainly due to the lattice O vacancies and superoxide oxygen ions (O₂^2-/O^-), which are generated by the transfer of lattice oxygen to adsorbed -OH and have performed excellent properties suitable for electrooxidation of analytes. However, the limited electron transfer kinetics, stability, and selectivity of perovskite oxides alone make perovskite oxides far from ready for scientific development. Therefore, composites of perovskite oxides with other materials like graphitic carbon, metals, metal compounds, conducting organics, and biomolecules are summarized. Furthermore, a brief section describing the future challenges and the corresponding recommendation is presented in this review.

Fabrication of SrTiO₃ Layer on Pt Electrode for Label-Free Capacitive Biosensors

Due to their interesting ferroelectric, conductive and dielectric properties, in recent years, perovskite-structured materials have begun to attract increasing interest in the biosensing field. In this study, a strontium titanate perovskite layer (SrTiO₃) has been synthesized on a platinum electrode and exploited for the development of an impedimetric label-free immunosensor for Escherichia coli O157:H7 detection. The electrochemical characterization of the perovskite-modified electrode during the construction of the immunosensor, as well as after the interaction with different E. coli O157:H7 concentrations, showed a reproducible decrease of the total capacitance of the system that was used for the analytical characterization of the immunosensor. Under optimized conditions, the capacitive immunosensor showed a linear relationship from to 1 to 7 log cfu/mL with a low detection limit of 1 log cfu/mL. Moreover, the atomic force microscopy (AFM) technique underlined the increase in roughness of the SrTiO₃-modified electrode surface after antibody immobilization, as well as the effective presence of cells with the typical size of E. coli.

Horseradish Peroxidase Immobilization on Amine Functionalized Carbon Nano Tubes: Direct Electrochemistry and Bioelectrocatalysis

Horseradish peroxidase (HRP) was successfully immobilized on amine functionalized TiO2-coated multiwalled carbon nanotubes (NH2 TiO2 CNTs) by a convenient and efficient method. Electrochemical impedance spectroscopy, cyclic voltammetry and amperometry were applied to characterize the HRP/NH2- TiO2 - CNT nano-composite. These techniques showed that the NH2 TiO2CNTs greatly enhance the electron transfer between HRP and the modified electrode. Owing to the redox reaction of the electroactive centre of HRP, the HRP/NH2-TiO2-CNTs modified electrode exhibited a pair of quasi-reversible peaks with a peak-to-peak separation (Δ Ep) of 70.6 m V and a formal potential ( E°’) of - 367.65 m V (versus Ag/AgCl) in phosphate buffer solution. The charge transfer coefficient (a) and the apparent charge transfer rate constant (ks) were found to be 0.34 and 2.08 s-1 respectively. The prepared biosensor responded to H2O2 with a linear range, detection limit, sensitivity and response time of 1.0 × 10−9 to 1.0 × 10 −7 M, 0.786nM, 28.4 μA A nM−1 and 3 s, respectively.

A selective novel non-enzyme glucose amperometric biosensor based on lectin-sugar binding on thionine modified electrode

A novel non-enzyme glucose amperometric biosensor was fabricated based on biospecific binding affinity of concanavalin A (Con A) for D-glucose on thionine (TH) modified electrode. TH can be covalently immobilized on potentiostatically activated glassy carbon electrode through Schiff-base reaction. Subsequently, the surface-adherent polydopamine film formed by self-polymerization of dopamine attached to TH and afforded binding sites for the subsequent immobilization of Con A molecules via Michael addition and/or Schiff-base reaction with high stability. Thus, a sensing platform for specific detection towards D-glucose was established. The binding of Con A towards D-glucose can be monitored through the decrease of the electrode response of the TH moiety. Due to the high affinity of Con A for D-glucose and high stability of the resulting sensing platform, the fabricated biosensor exhibited high selectivity, good sensitivity, and wide linear range from 1.0×10(-6) to 1.0×10(-4) M with a low detection limit of 7.5×10(-7) M towards D-glucose.

Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase based on gold nano-seeds dotted TiO2 nanocomposite

Gold nano-seeds (GNSs) (capital EF, Cyrillic=2-5 nm) were dotted in TiO(2) colloids and the horseradish peroxidase (HRP) was successfully immobilized on the as-made GNSs-TiO(2) nanocomposite by a convenient and effective method. The matrix integrates the merits of both GNSs and TiO(2), which provides a favorable microenvironment for the immobilization of HRP. The cyclic votammetric results demonstrated that the entrapped HRP achieves direct electron transfer at glassy carbon electrode (GCE). A pair of stable and quasi-reversible redox peaks with a small peak-to-peak separation of 43 mV was observed in phosphate buffer solution. The GNSs stabilized by TiO(2) colloids acted sufficiently as the conducting tunnel to promote the electron transfer. As a result, the electrochemical behaviors were improved in virtue of the synergic effect of TiO(2) and GNSs. The Nafion/HRP-GNSs-TiO(2)/GCE displayed an excellent and rapid electrocatalytic response to the reduction of H(2)O(2). The proposed biosensor exhibited a good linear response in the range from 4.1 x 10(-5) to 6.3 x 10(-4) mol L(-1), with a detection limit of 5.9 x 10(-6) mol L(-1) (at the ration of signal to noise, S/N=3). The apparent Michaelis-Menten constant was estimated to be 0.63 mmol L(-1). Furthermore, the biosensor possesses satisfactory stability and good reproducibility.

A novel protocol for covalent immobilization of thionine on glassy carbon electrode and its application in hydrogen peroxide biosensor

A novel protocol for effectively covalent immobilization of thionine (Th) was proposed, which was based on Schiff-base reaction between -NH(2) of Th and -COH which was in situ generated on glassy carbon electrode (GCE) via simple potentiostatic activation in diluted nitric acid. GCE pretreated by potentiostatic activation possessed CHO-riched surface and microporous structure with high distribution density of electron transfer sites, and thus it became a good candidate for effective immobilization of Th through imine bond with high stability. The application of the resulting Th modified electrode in hydrogen peroxide biosensor was also investigated and it exhibited rapid response to H(2)O(2) within 3s. The linear calibration ranged from 5.0x10(-7) to 5.8x10(-3)M with a detection limit of 1.0x10(-7)M. The effective immobilization of Th on potentiostatically activated GCE surface has deep significance in mediator immobilization, on which further researches based are under way.