Sensors & Transducers Journal, Vol. 113, Issue 2, February 2010, pp. 1-17
computers  using quantum dots or single-electron transistors, which are 10,000 times smaller than the current ones. Colloidal gold, iron oxide crystal, and semiconductor quantum dots having sizes 1-20 nm, have showed unique diagnostic applications in biology, medicine, and agri-biotechnology .
The domain of nanotechnology encompasses a very important area called “nanomedicine”, which is concerned with the development of minimally invasive and targeted delivery of diagnostic, pharmaceutical and therapeutic agents to various body organs, tissues, and cells in a controlled manner . Research in nanomedicine includes three important aspects: (i) nanosensors, (ii) nanofluidics and (iii) lab-on-a-chip. Nanosensors consist of nanostructured particles, or nanoparticles, or nanodevices that respond to physical, chemical, or biological stimuli. Nanofluidics is concerned with navigation, mixing, and controlled delivery of nanoliter volume of fluids through microchannels on a chip . Lab-on-a-chip integrates sensors, fluidics, optics and electronics on a silicon chip to be used as a biochip for drug delivery systems or for biochemical diagnostics or DNA detection [9, 42-45, 86-88, 119, 120].
During the early eighties, powerful microscopes were invented, which could scan the surface of the specimen using physical probes to produce images of the surface at the nanometer region. Several simultaneous interactions can also be imaged with these microscopes. Some microscopes used electron beams for studying surface topography, compositions and also other properties of a sample. These powerful microscopes like Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), Tunneling Electron Microscope (TEM), etc., helped not only to understand and study materials at the nanoscale region, but also to pick them up and move them around to form basic nanostructures, allowing some materials to be built molecule by molecule.
For the past several years, various materials have been developed whose dimension lies in the nanoscale region, such as, inorganic nanocrystals or quantum dots (QD), nanoparticles, nanocomposites, different nanostructured materials and many other for sensor applications. In the nano region, materials nomenclatures, i.e. wire, dots, quantum well etc., are defined according to the size of the crystals and the way the atoms are arranged in it. Nanostructured materials show interesting optical, electronic and catalytic properties.
Among the nanostructured materials, porous silicon (PS) shows very amazing features like biocompatibility, biodegradable, electroluminescence (EL), and photoluminescence (PL) at room temperature. It also shows non-toxic behavior when applied to human body. These unique properties of PS make it particularly suitable for biosensor application and also as a drug delivery material for in vivo applications. Sailor and his group reported a review on PS where it has been used as a drug delivery material . Nanostructured porous silicon (PS) is also used to create optical biosensors, DNA detection sensors and photodetectors. A review on the scope of PS in nanotechnology has been reported by C.A. Betty . As PS is fabricated from Si wafers, its production cost is considerably lower and can be easily integrated with electronic equipments to produce a link between CMOS technology and photonic devices to create smart sensors and biochips.
From the inorganic nanocrystal category, the luminescent semiconductor nanocrystals or quantum dots (QDs) appears to be very promising material in the biosensor industry. QDs generated a huge interest in the biosensing industry due to their excellent fluorescent properties which may help in eliminating the problems faced during the use of conventional organic or protein based fluorophores.
Luminescent porous silicon nanoparticles were also synthesized and studied as a replacement of fluorescent dyes and for in vivo applications as a drug delivery system.