Other standard methods such as high-performance liquid chromatography (HPLC) [2,17�C23] and gas chromatography (GC) [24,25] are well known for formaldehyde detection where 2,4-dinitrophenylhydrazine is commonly used as a derivitization agent for such techniques. Both chromatographic and colorimetric methods suffer to certain extent interference from other carbonyl substances, especially acetaldehyde and acetone, not to mention the fact the detection techniques involve tedious derivative procedures and the use of expensive and complicated instrumentation [26].On the other hand, biosensors show potential for complementing both laboratory-based and field analytical methods for food monitoring.
Enzyme immobilization is one of the most important facets in biocatalysis-based biosensors research.
When an enzyme is immobilized in a polymer matrix, access of analyte or products via diffusion must occur, but the enzyme should be retained. Covalent immobilization via polymer matrices benefits from the loss prevention of enzymes and sometimes better enzyme stabilization [27]. Application of nano/micro-sized matrix materials for covalent enzyme attachment is becoming popular because of their large surface area, which improves the enzyme binding capacity and increases the mass transfer kinetics when the enzymatic reaction occurs at the surface of nano/micro-sized matrix materials, compared with in the polymer film matrix [28].Most reported sensors based on polymer microspheres were ion sensors [29�C36].
Polymeric microspheres and nanospheres have been used for enzyme immobilization but their application to biosensor is still rather unexplored.
Bayramo?lu Carfilzomib et al. [37] have used poly(2-hydroxyethyl methacrylate-co-N-methacryloly-l-histidinemethylester) microspheres containing l-histidine groups chelated with Ni(II) ions for urease immobilization GSK-3 and found that there was an increase in enzyme stability and improvement in the range of optimum enzyme operational temperature. Brahim et al. [38] immobilized glucose oxidase into crosslinked poly(hydroxyethyl methacrylate-co-dimethylaminoethyl methacrylate) hydrogel microspheres and confirmed that the hydrogel microsphere matrix presented no significant diffusional barrier to enzyme-substrate reaction.
Polymeric nanospheres from thiol-functionalized poly(divinylbenzene-co-acrylic acid) have been used for self-assembly of gold nanoparticles and horseradish peroxidase immobilization to fabricate amperometric biosensors for hydrogen peroxide detection. The resulting biosensors showed a large improvement in linear range, exhibited high sensitivity, good reproducibility, and long-term stability [39�C41].