A simple and reliable one-pot approach was established for the development of a novel hydrogen peroxide (H2O2) biosensor based on in situ covalent immobilization of horseradish peroxidase (HRP) into biocompatible material through polysaccharide-incorporated sol–gel process. Siloxane with epoxide ring and trimethoxy anchor groups was applied as the bifunctional cross-linker and the inorganic resource for organic–inorganic hybridization. The reactivity between amine groups and epoxy groups allowed the covalent incorporation of HRP and the functional biopolymer, chitosan (CS) into the inorganic polysiloxane network. Some experimental variables, such as mass ratio of siloxane to CS, pH of measuring solution and applied potential for detection were optimized. HRP covalently immobilized in the hybrid matrix possessed high electrocatalytic activity to H2O2 and provided a fast amperometric response. The linear response of the as-prepared biosensor for the determination of H2O2 ranged from 2.0 × 10−7 to 4.6 × 10−5 mol l−1 with a detection limit of 8.1 × 10−8 mol l−1. The apparent Michaelis–Menten constant was determined to be 45.18 μmol l−1. Performance of the biosensor was also evaluated with respect to possible interferences. The fabricated biosensor exhibited high reproducibility and storage stability. The ease of the one-pot covalent immobilization and the biocompatible hybrid matrix serve as a versatile platform for enzyme immobilization and biosensor fabricating.

A novel and simple strategy for fabricating of DNA electrochemical biosensor was developed based on covalent coupling of probe NH2–ssDNA (S1) on Au electrode that had been functionalized by diazotization of assembled 4-aminothiophenol (4-ATP) monolayer. The thiol group of 4-ATP allowed the stable assembly of 4-ATP monolayer. The following diazotization reaction was directly performed to prepare functional diazo–ATP film for covalent coupling of probe S1. Remarkably, it was noting that the diazo–ATP provided a surface with high conductibility for electron transfer. The complementary ssDNA was determined by using differential pulse voltammetry. The linear range of the developed biosensor was from 1.57 × 10−9 to 4.52 × 10−7 M with a detection limit of 3.26 × 10−10 M. The fabricated biosensor possessed good selectivity and could be regenerated. The covalent immobilization of probe S1 by simple diazotization-coupling on self-assembled 4-ATP monolayer could serve as a versatile platform for DNA immobilization and biosensors fabricating.

One-step construction of horseradish peroxidase (HRP) and glucose oxidase (GOD) bienzyme biosensor was established based on a simple and controllable electrodeposition approach by in-situ formation of biocomposite film on electrode. With hydrogen peroxide (H2O2) instantly generated by GOD-catalyzed oxidation of glucose, quantitative measurement of glucose could be achieved. In the proposed electrodeposition strategy, Concanavalin A (Con A) was applied as bifunctional cross-linker for in-situ incorporating of HRP–GOD in biocompatible chitosan (CS) matrix due to its biospecific affinity interaction with CS and glycoproteins. Scanning electron microscopy showed that the HRP–GOD/Con A/CS biocomposite film possessed highly porous surface. The developed bienzyme biosensor exhibited a fast amperometric response for the determination of glucose. The linear response of the developed biosensor for the determination of glucose ranged from 1.0 × 10−6 to 2.2 × 10−4 M with a detection limit of 6.7 × 10−7 M. The biosensor can be used to determine glucose in serum directly. The biosensor presented high stability owing to the design of the introduction of Con A and instant generation of H2O2 with bienzyme system. The one-step construction of biosensor based on non-manual technique in biocompatible environment was direct and facile.

An interfacial organic–inorganic hybridization concept was applied to the preparation of a new spherical imprinted material for protein recognition. The functional biopolymer chitosan (CS), shaped as microsphere and high-density cross-linked, constituted of the polysaccharide core for surface imprinting. After the model template protein, bovine serum albumin, was covalently immobilized by forming imine bonds with the functional amine groups of CS, two kinds of organic siloxane (3-aminopropyltrimethoxysiloxane: APTMS, and tetraethoxysiloxane: TEOS) assembled and polymerized on the polysaccharide–protein surface via sol–gel process in aqueous solution at room temperature. After template removal, the protein-imprinted sol–gel surface exhibited a prevalent preference for the template protein in adsorption experiments, as compared with four contrastive proteins. Bioinformatics methods were also employed to investigate the imprinting process and the recognition effect. The influence of siloxane type, pH, siloxane/water ratio on template removal and recognition selectivity was assessed. Under optimized imprinting conditions, a large quantity of well-distributed pores was observed on the immobilized-template imprinted surface. The surface-imprinted adsorbent offered a fast kinetics for template re-adsorption and could be reused. Compared with the imprinted material prepared with free-template, material prepared with immobilized-template possessed higher adsorption capacity towards template protein. Easy preparation of the described imprinted material, high affinity and good reusability make this approach attractive and broadly applicable in biotechnology for down-stream processing and biosensor.

In this article interaction of transition metal complexes with DNA and its applications in electrochemical DNA biosensors as hybridization indicator or electroactive marker of DNA are reviewed. Special emphasis has been given to the efforts for the development of new transition metal complexes and their interaction to DNA. DNA and polymers covalently conjugated with transition metal complexes were also reviewed.

A new porous sorbent for wastewater treatment of metal ions was synthesized by covalent grafting of molecularly imprinted organic–inorganic hybrid on silica gel. With sucrose and polyethylene glycol 4000 (PEG 4000) being synergic imprinting molecules, covalent surface coating on silica gel was achieved by using polysaccharide-incorporated sol–gel process starting from the functional biopolymer, chitosan and an inorganic epoxy-precursor, gamma-glycidoxypropyltrimethoxysiloxane (GPTMS) at room temperature. The prepared porous sorbent was characterized by using simultaneous thermogravimetry and differential scanning calorimeter (TG/DSC), scanning electron microscopy (SEM), nitrogen adsorption porosimetry measurement and X-ray diffraction (XRD). Copper ion, Cu2+, was chosen as the model metal ion to evaluate the effectiveness of the new biosorbent in wastewater treatment. The influence of epoxy-siloxane dose, buffer pH and co-existed ions on Cu2+ adsorption was assessed through batch experiments. The imprinted composite sorbent offered a fast kinetics for the adsorption of Cu2+. The uptake capacity of the sorbent imprinted by two pore-building components was higher than those imprinted with only a single component. The dynamic adsorption in column underwent a good elimination of Cu2+ in treating electric plating wastewater. The prepared composite sorbent exhibited high reusability. Easy preparation of the described porous composite sorbent, absence of organic solvents, cost-effectiveness and high stability make this approach attractive in biosorption.

A new voltammetric enzyme-linked immunoassay system of 3,4-diaminobenzoic acid (DBA)–H2O2–horseradish peroxidase (HRP) for sensitive detection of prostate specific antigen (PSA) in human serum was present. In the proposed procedure, labelled HRP efficiently catalyzed the oxidation reaction of DBA by H2O2 and generated the electroactive product, 2,2′-biamino-4,4′-bicarboxyl azobiphenyl, which produced a sensitive second-order derivative linear sweep voltammetric peak at potential of −0.62 V (versus SCE) in Britton–Robinson (BR) buffer solution. The linear range for detection free HRP was from 4.0 × 10−12 to 4.0 × 10−9 g ml−1 and the detection limit was about 6.0 × 10−13 g ml−1. The proposed new system could be used for detection of PSA ranging from 0.20 to 16.0 ng ml−1 with a detection limit of 0.10 ng ml−1, which was five times lower than that of the traditional o-phenylendiamine spectrophotometric enzyme-linked immunosorbent assay (ELISA) method. The proposed electrochemical ELISA method is simple, inexpensive, reproducible and sensitive, which shows potential for detecting PSA in clinical diagnosis.

Ion-imprinting concept and polysaccharide incorporated sol–gel process were applied to the preparation of a new silica-supported organic–inorganic hybrid sorbent for selective separation of Cd(II) from aqueous solution. In the prepared shell/core composite sorbent, covalently surface coating on the supporting silica gel was achieved by using a Cd(II)-imprinting sol–gel process starting from an inorganic precursor, γ-glycidoxypropyltrimethoxysiloxane (GPTMS), and a functional biopolymer, chitosan (CS). The sorbent was prepared through self-hydrolysis of GPTMS, self-condensation and co-condensation of silanol groups (Si-OH) from siloxane and silica gel surface, in combination with in situ covalent cross-linking of CS with partial amine shielded by Cd(II) complexation. Extraction of the imprinting molecules left a predetermined arrangement of ligands and tailored binding pockets for Cd(II). The prepared sorbent was characterized by using X-ray energy dispersion spectroscopy (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Batch experiments were conducted to study the sorption performance by removal of Cd(II) when present singly or in binary system, an aqueous Cd(II) and Zn(II) mixture. The ion-imprinted composite sorbent offered a fast kinetics for the sorption of Cd(II) and the maximum capacity was 1.14 mmol g−1. The uptake capacity of the imprinted sorbent and the selectivity coefficient were much higher than that of the non-imprinted sorbent. The imprinted sorbent exhibited high reusability. The prepared functional sorbent was shown to be promising for the preconcentration of cadmium in environmental and biological samples.