The study of complex biological interactions in the field of biology has been focusing on labelling or staining. Fluorescent labelling of biomolecules has become indispensable tool in biological studies. The types of fluorescent labelling agents have been to use organic fluorosphores such as fluoresce in and cyanine dyes.
The rapid advances in biological science have accelerated the analysis of bio-molecules such as polypeptides, proteins and nucleic acids has led to the development of sensitive detectable signals. Radio-immuno assay methods have been introduced for their high sensitivity of 10-9 – 10-12 with a wide application range.
New types of inorganic nano-particles such as QDs (quantum dots) and novel fluorescent latex/silica nano beads have been developed. The new class of fluorescent labels has become popular due to their better optical properties like enhanced photo – stability and a larger stokes shift over the conventional organic fluorosphore.
The latest method is to use inorganic nano particles called semiconductor quantum dots (QDs) which are semiconductor nano crystals composed of atoms from groups II – VI or III – V of the periodic table. Physical dimension is 1 – 5 nanometers. Due to this small size of only few nanometers which is the same order of magnitude as the de Broglie wavelength of electrons and holds at the room temperature, the state of free charge carriers is quantized and movement is determined by quantum mechanics. The small size of these QDs leads to quantum confinement effect which endows nano crystals with unique optical and electronic properties.
The QDs are mostly synthesized in organic solvents and it was focused on opto-electronic devices, quantum dot lasers and high density memory. Dr. Alivisatos and Nie simultaneously discovered in 1998 the water soluble system that can be conjugated with bio-molecules. The advantage of using QDs a fluorescent labels are enhancement of sensitivity and stability lover conventional organic fluorosphores that re 20 times brighter and more stable against photo bleaching. The other advantage is the onset of absorbance and emission maxima of QDs shift with a change in size of QDs or chemical composition.
Thus the wavelength of emission can be tuned by altering their size and chemical composition. Unlike conventional fluorosphores, QDs exhibit continuous absorption profiles and can be excited efficiently at any wavelength shorter than emission peak. This leads to multiplexing detection studies. The QDs emission could be size-tuned to improve spectral overlap and emit light at slow rate to eliminate most of the auto-fluorescence in the back ground but fast enough to maintain a high photon turnover rate.
Thus these unique optical properties of QDs make them excellent labels in biological investigations. A wide range of bio-molecules including DNA (Deoxy-ribose nucleic acid) the genetic material that can be used in medical studies such as in vitro detection assays, tissue imaging in selective and generalized imaging of live cells and organisms. A multi-functional QD probe linked with tumor-targeting antibodies for targeting cancer and imaging. Though the potential and success in biology are wide, some limitations like optical blinking make them in quantitative estimations. QDs themselves are not biocompatible and their surface has to be modified before they are used in cellular and animal studies when the best photo-suitability is with regard to photo stability. QDs possessing a narrow, tunable and symmetric emission spectrum open new possibilities in diagnostics.
Microbial production of nano particles
Nano particles exhibit unique electronic, magnetic, catalytic and optical properties that are totally different from those of bulk materials which can be exploited for diverse applications in human activity spectrum as well remediation of deterioration of air, water and soil e.g. bioleaching and bioremediation.
The recently developed nano particle production by microbes has led to revolutionary feature to exploit then use. This method is highly competitive, cheaper than the present chemical synthesis.
Many microbes are known to produce inorganic nano particles as compared to the present chemical synthesis i.e. costlier. Both the methods produce with control on size, shape, composition of particles. Magnetotactic bacteria produce magnetic nano particles, silver nanos by Pseudomonas stutzeri, semi conducting cadmium sulphide crystals by yeast – schizo, Saccharomyces pombe, palladium nano particles by sulphate reducing bacteria in the presence of exogenous electron donor. The ability of bacteria, fungi, actinomycetes, yeast, algae and plants to accumulate gold ions from the solutions has been reported. Gold nano particles have been produced by bacillus species, fungal species such as Verticillium and Fusarium, actinomyces such as Rhodococcus and Thermanospora and lactic acid bacteria.
Synthesis of nano structures such as nano wires and the assembly of nano particles using biological templates such as DNA, proteins, S-layers and viruses have been successfully developed for the immense application to commence the new era of nanotechnology in 21st century.
Potential of nanotechnology in blood vessel formation
Angiogenesis is the natural physiological process to the formation of new capillaries from the existing blood vessels that plays a significant role in the development of embryo, healing of wounds besides playing the role in the control of Ischaemic cardiovascular diseases which is aided by some proteins, cytokines like vascular endothelial growth factors. Growth factors are also associated with the proliferation of tumours, fibrosis and thrombosis.
Zinc oxide nano materials have been found to stimulate endothelial cells which have been confirmed in the blood vessel formation in chick embryo by in vivo studies. Experiments with mice involving the use of nano rods of Europium hydroxide when injected into zebra fish established the formation of nano blood vessels with out any side effects. Studies with Europium hydroxide nano rods on the liver, kidney, spleen and other organs in mice with out any previous history showed no side effects.
The excellent research work done by Dr.Chittaranjan Patra at IICT, Hyderabad has contributed significantly that has the immense potential to treat cardiovascular, ischaemic diseases by Europium hydroxide nano rods. There were no previous studies on the toxicity of nano rod material in liver, kidney and spleen. Their continued research in the field is likely to revolutionize the diseases emanating from blood vessels.
Nano-sensors for pathogen and contaminant detection
At present we have sensors to provide enormous information about parameters like temperature, data on weather and transportation by sea, land and air besides chemical contaminants etc. Living organisms have the ability to sense the environment. Human beings sense the environment through sight, touch, taste, smell and sound – the five senses. Human ear uses nano structures to transduce the macro motion of ear drum induced fluid motion into chemical/electrical signal. In living organisms sensors operate over a range of scales from the macro (ear drum variations) to the micro (nerve cells) and to the nano scale (molecules binding to receptors in nose).
A combination of biology and nano scale technology into sensors holds the great potential of increasing the sensitivity thereby leading to a significantly reduced response time to sense the potential problems. For example: a bio-analytical nano-sensor that can detect a single virus particle long before the virus multiplies and precipitates the symptoms in plants and animals.
Some of the potential areas for the application of bio-analytical sensors are the detection of pathogens, contaminants, environmental characteristics like light/dark, hot/cold, wet/dry, heavy metals and particulates or allergens. It is possible to detect a single virus or foreign particle at an opportune time is the real challenge.
The bio-sensors have to be equipped with desirable characteristics that are small, portable, rapid response and processing (real time) specific, quantitative, reliable, accurate, reproducible, robust and stable.
The most important areas of programme are to develop pathogen, nutrient and contaminant detection systems so as to obtain an improved understanding of nano scale sensor mechanism through research and modelling. The detection systems are for pathogens, nutrient deficiency or contaminants, remote and continuous sensing of agricultural products during production in various environmental settings, nucleic acid engineering-based probes and methods of amplification of signals for the detection of pathogens or contaminants, laboratory bio-sensors to detect pathogens on the farm, pathogens, viruses, chemicals and finally the laboratory bio-sensors to detect proteins and genetically modified organisms.
India has to invest more money on the basic and applied research in nanotechnology. BARC (Bhabha Atomic Research Centre) of the Department of Atomic Energy, Government of India based at Mumbai has done extensive work on the production of nano silver that can be used extensively in medicine and health.
Nano silver to treat Gonorrhoea
Today the situation is that antibodies developed a decade ago or so have become useless as the bacteria developed resistance. This is due to a feature called mutation in the genome of microbe.
The present situation is that many microbes have developed resistance to antibodies. The latest is gonorrhoea which has become drug resistant. During 2002, 15 per cent of gonorrhoea patients were found to be resistant to antibiotic Cefixime and by 2010 the situation accelerated to 17 per cent which has to be treated by a high dose of Ceftriaxone and Azithromycin that reduced the resistance to 11 per cent with in a year.
The latest situation is that any disease caused by bacteria or even viruses can be prevented by the administration of nano silver. Thus nano silver has become a universal killer of microbes.