There is increased demand both in developed and the developing countries for ready availability of biosensors 1-5. In this context, self-assembled monolayer (Scheme I) based biosensors have recently attracted much interest due to their applications in health care, environmemtal, pharmaceuticals and food industry etc. This has been attributed to the use of ultra-thin layers for immobilization of desired sensing elements that may result in faster and stable biosesning devices. Biosensor has three major components: (i) a bio-recognition element such as DNA, enzyme, antibody etc. for recognition of an anlyte, (ii) a matrix such as a self-assembled monolayer (SAM), Langmuir-Blodgett film, thick polymer film, hydrogel and nanomaterials etc. for the immobilization of a biomolecule and (iii) a transducer unit for conversion and amplification of the biochemical reaction product into a recognizable. For fabrication of biosensors 1, appropriate immobilization of signal biomolecules on a transducer surface is presently a major area of concern. The thrust is, however, shifting towards the utilization of SAMs as matrices for proper and oriented immobilization of biomolecules. Using a SAM to functionalize noble metal surfaces provides a simple route to functionalize electrode surfaces by organic molecules (both aliphatic and aromatic) containing free anchor groups such as thiols, disulphides, amines,silanes, or acids for the immobilization of biomolecules. Among the various biochemical analytes such as glucose, galactose, uric acid, urea etc in biological samples to monitor human health, estimation of cholesterol has acquired the maximum attention since it is an indicator of abnormality in lipid metabolism and its abnormal level is associated with coronary artery disease, diabetes mellitus, hypothyroidism, anemia and wasting syndromes etc 2. I will focus on some of the recent developments that have occurred in our laboratories in the area of self-assembled monolayers based biosensors for cholesterol sensing 3-5.
Scheme 1. (a) Gold plate, (b) gold surface having terminal C–H group of P3HT SAM, © 1-fluro-2-nitro-4-azido-benzene modified SAM using nitrene reaction and (d) immobilized ChOx on SAM by displacing labile fluoro group at 37 ◦C. S.K. Arya et al., Biosensors and Bioelectronics 22 (2007) 2516–2524 2519.
- Biosensors for clinical diagnostics industry, B.D.Malhotra and A.Chaubey, Sensors & Actuators B, 2003,Volume 91, pp117-127.
- Recent advances in cholesterol biosensor, Sunil.K.Arya,M.Datta and B.D.Malhotra, Biosensors & Bioelectronics 2008,Volume 23, 1083–1100.
- Dithiobissuccinimidyl propionate self assembled monolayer based cholesterol Biosensor , S.K. Arya, P.Pandey, S.P.Singh, M.Datta and B.D.Malhotra ,Analyst, 2007, 132, 1005-1009.
- Application of self-assembled monolayer of 10-carboxy-1-decanethiol for cholesterol biosensor, P.R.Solanki, S.K.Arya, Y.Nishimura,M.Iwamoto, B.D.Malhotra, Journal of Biomedical & Pharmaceutical Engineering 2008, 7-13.
- Biosensor for total cholesterol estimation using N-(2-Aminoethyl)-3- Aminopropyl-trimethoxysilane self-assembled monolayer, S.K.Arya,M.Datta, S.Singh, B.D.Malhotra, Analytical & Bioanalaytical Chemistry,2008, Volume 8,2235-2242.
Centre for Cellular and Molecular Biology, Hyderabad, India