Mini Review Biosensors for heavy metals Neelam Verma* & Minni Singh* Biosensor Development Laboratory, Department of Biotechnology, Punjabi University, Patiala – 147 002, Punjab, India; *Authors for correspondence (Tel.: +91-175-2825708; Fax: +91-175-2283073; E-mail: minni_singh@yahoo.com, neelam_verma2@rediffmail.com) Received 5 June 2004; accepted 25 August 2004; Published online: March 2005 Key words: biosensors, environmental monitoring, heavy metals Abstract A biosensor is an analytical device that consists of an immobilized biocomponent in conjunction with a transducer, and represents a synergistic combination of biotechnology and microelectronics. This review summarizes the use of biosensors for detecting and quantifying heavy metal ions. Heavy metal contami- nation is of serious concern to human health since these substances are non-biodegradable and retained by the ecological system. Conventional analytical techniques for heavy metals (such as cold vapour atomic absorption spectrometry, and inductively coupled plasma mass spectrometry) are precise but suffer from the disadvantages of high cost, the need for trained personnel and the fact that they are mostly laboratory bound. Biosensors have the advantages of specificity, low cost, ease of use, portability and the ability to furnish continuous real time signals. The analysis of heavy metal ions can be carried out with biosensors by using both protein (enzyme, metal-binding protein and antibody)-based and whole-cell (natural and genetically engineered microorganism)-based approaches. Introduction Biosensors – a synergistic combination of biotechnology and microelectronics A biosensor is an analytical device that consists of an immobilized biological material in intimate contact with a compatible transducer, which will convert the biochemical signal into a quantifiable electrical signal (Gronow 1984). Biosensors are the offspring of the first successful marriage between biotechnology and modern electronics. The bio- molecules are responsible for the specific recogni- tion of the analyte whereas the physicochemical transducer supplies an electrical output signal which is amplified by the electronic component (Scheller & Schubert 1992). The specificity of en- zymes is the main reason for their use in biosen- sors. Since most of the enzymes employed for use in sensors have been isolated from microorgan- isms, it is logical that the organisms themselves should be regarded as potential biocatalysts (Aston & Turner 1984). In microorganisms, the enzymes remain in their natural environment, increasing stability and activity (Guilbault 1984; Corcoran & Rechnitz 1985; Luong et al. 1988; D’Souza 2001; Verma & Singh 2003). Cell mem- branes and organelles can also be used for biosensor construction (Burstein et al. 1986, Verma & Malaku 2001). Specific binding between antibody and antigen can be exploited in immu- nobiosensors. To detect very low concentrations of substances such as drugs, toxins or explosives, receptor-based sensors are very appealing (Prasad et al. 2004). Various immobilization procedures have been used in biosensor construction. In general, the choice of procedure depends on the nature of the biological element, the type of transducer used, the physicochemical properties of the analyte and BioMetals (2005) 18:121–129 Ó Springer 2005 DOI 10.1007/s10534-004-5787-3