Biosensors gold surfaces

In 1994, thiols were firstly used as stabilizers of gold nanoparticles [6a]. Thiols form monolayer on gold surface [18] and highly stable nanoparticles could be obtained. Purification of nanoparticles can be carried out, which makes chemical method of metal nanoparticles a real process for nanomaterial preparation. Various thiol derivatives have been used to functionalize metal nanoparticles [6b, 19]. Cationic and anionic thiol compounds were used to obtain hydrosols of metal nanoparticles. Quaternary ammonium-thiol compounds make the nanoparticle surface highly positively charged [20]. In such cases, cationic nanoparticles were densely adsorbed onto oppositely charged surfaces. DNA or other biomolecule-attached gold nanoparticles have been proposed for biosensors [21]. 

Pre-treatment of the transducer surface with PAH increased the amount of the immobilized Ag and the response of the immune biosensor was much more stable in comparison with the bare gold surface. The sensor with Ag immobihzed after pre-treatment with PAH served for 2 months versus 2-3 weeks for Ag deposited on the bare surface. Ag immobilization on the PAH layer increased the sensitivity of the immune biosensor by 15-20% in comparison with Ag immobilized on the bare surface. At the same time dodecanethiol did not affect the biosensor sensitivity but increased its service life. 

Duan et al. used a monolayer of thioctic acid to covalently immobihse monoclonal antibodies to a gold electrode while performing amperometric analysis [28]. Frey et al. demonstrated potential biosensor application of this immobilisation method by binding polylysine to gold surface plasmon resonance (SPR) electrodes via a SAM of 11-mercaptoundecanoic acid [29]. 

Deng I and Enke C 1980 Adenosine-selective electrode Anal. Chem. 52 1937-40 DeBono R F, Krull U J and Rounaghi Gh 1992 Concanavalin A and polysaccharide on gold surfaces Biosensor Design and Application ed P R Mathewson and J W Finley (Washington, DC American Chemical Society) pp 121-36... 

FIA as such is available from a few different suppliers. Reactors filled with immobilized enzymes are also commercially available. More sophisticated equipment based on the FIA concept is the BIACORE from Pharmacia Biosensor. Here a gold surface covered with a carboxydextran is used as reactor for binding reactions. The reading is done by means of evanescent wave technology [63]. The BIACORE illustrates one step in the direction of miniaturization of the analytical unit. As the understanding of the chemistry and the analytical protocol becomes available, much may be gained by miniaturization [64]. 

A novel quartz crystal microbalance method has been described, which measures the concentration of the antibiotic chloramphenicol, via antichloramphenicol antibodies, which were covalently coupled to the monolayer on a gold surface [44], While this approach shows some promise, the system described was of low sensitivity, detecting only in the pM range. The development of highly sensitive recombinant antibody fragments to atrazine [45] and their potential for expression in multiple different structural formats [46] will greatly aid the development of rapid biosensors for environmental contaminants in the future. 

The characteristic electrochemical behavior of enzyme, protein and Upid monolayers adhered to SAMs derived from thiols on gold surfaces may be applied to the development of biosensors. The gold electrodes resulting from incorporation of monensin (203) and vaUnomycin (204) into bilayers, consisting of the SAMs of aUsanethiol covered by a Upid monolayer, have high sensitivity for monovalent ions . A gold electrode with a SAM of a modified /3-cyclodextrin was proposed for electrochemical detection of organic compounds . 

---