Nanotechnology-based techniques are gaining impetus in forensics investigation; these techs also represent novel techniques for detection and identification
DR CHETAN LAVU KAREKAR
Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is about 1 to 100 nanometers. Nanoscience and nanotechnology are the study and application of extremely small things and can be used across all the other science fields, such as chemistry, biology, physics, materials science, and engineering (National Nanotechnology Initiative, NNI).
Nanotechnology entails the development of novel nanomaterials that exhibit starkly different properties from their bulk counterparts. This has resulted in nanotechnology being employed in numerous fields including forensics. Nanotechnology contributes to forensic sciences in two ways. The instruments traditionally used to analyze forensic evidence have detection limits which can be overcome by using instruments that can operate at nano-scale (Transmission electron microscope, scanning electron microscope, atomic field microscope, micro-fluidic devices etc.).
Besides the unique physicochemical properties of nanomaterials can help in collection and detection of evidence which may be difficult to acquire (Shukla, 2013). Nanotechnology can not only be regarded as a tool for forensic examination, but it can also be used for forensic characterization of certain pieces of evidence collected at the crime scene. Thus the extent of utilization of nanotechnology in forensics is magnanimous.
As mentioned above, the instruments used to characterize nanomaterials or that require sample sizes in nano range have been used successfully to analyze forensic evidence. In order to determine the origin of certain forensic evidence available at a very small sample size either electron/ atomic force microscopes are needed or micro-fluidic devices that can detect the presence of a biological sample. For example inks of inkjet printers are now manufactured with specific fluorescent/ non- fluorescent nanoparticles which can be either analyzed using electron microscopes that help the forensic experts to profile the ink and determine its origin (Shukla, 2013).
Anti-counterfeiting inks containing specific nanoparticles are being used as inks in currency notes or as security tags in passports and credit cards. The forgery of such documents become difficult as the nanoparticles cannot be seen with naked eyes or even through a normal optical microscope.
The detection of such anti-counterfeiting inks is only possible through electron/ atomic force microscope which are extremely expensive and available only in laboratory set-ups. Similarly, minuscule quantities of mitochondrial DNA samples can be analyzed post PCR amplification by utilizing analyzers that have sample size requirement in nano-litres range. One such instrument most popularly used is Agilent 2100 bioanalyzer, which uses an array of multiple channels to inject and quantify nanoliter amounts of 12 double-stranded DNA samples in less than 30 minutes.
On account of their small size the potential of these devices for forensic applications increases manifold (McCord, 2006). Similarly, another
important aspect of forensic investigation includes gunshot residue (GSR) analysis which now entails determining the elemental composition of the nanoparticles present in the GSR. The thumb rule GSR is that it spreads up to 6-8 inches in case of short-range, 36 inches away from the bullet hole for long-range and 8-18 inches for medium range and by looking at the shape, size and the composition of the nano-particulate GSR the distance from which the gun was fired can be determined.
Nanotechnology has revolutionized one particular area in forensics, i.e. fingerprint extraction. It is this area that nanomaterials and nanotechnology have contributed the most. Despite the plethora of modern physical and chemical fingerprint-detection techniques (Hazarika and Russell, 2012), a considerable portion of the latent fingermarks still escape detection. A plausible explanation is the remarkable difference in sweat composition between individual persons (Jaber et al. 2012). The latent fingerprint/fingermark detection involves either the binding of the luminescent/ non-luminescent nanoparticle preparation to the fingermark for positive development or to the area around the fingermark to give a negative development. As nanometer-sized particles have the potential to adhere to the fingermark deposit better than the bulk particles, due to their greater surface area-to-volume ratio, the nanomaterials represent a more attractive alternative for fingermark development (Theaker et al. 2008).
Nanotechnology also enables the synthesis of conventional fingermark reagents at nanoscale to enhance resolution. For example, functionalized gold nanoparticles (AuNPs) were shown to be superior to traditional colloidal gold (non-functionalized AuNPs) in metal deposition methods (Dilag et al. 2011). Besides, the AuNPs, numerous luminescent nanoparticles such as ZnO, and quantum dots (QDs) may be used for fingermark extraction without the need for silver-deposition detection (Dilag et al. 2011). Most of these nano preparations not only enable fingerprint extraction and detection under wet conditions but also in presence of bodily fluids such as sebaceous secretions and/ or blood (Jaber et al. 2012; Shukla, 2013).
Fluorescent zinc oxide (ZnO) nanoparticles have been successfully used for fingerprint extraction and detection as these nanoparticles possess inherent UV-fluorescence. Besides, these self fluorescent nano-preparations, researchers have developed fluorescent dye-doped nanoparticles that provide improved resolution and enhanced contrast. For example, aluminium oxide (AlO2) nanopowder coated with two layers, first layer of bean seed extracts and a second of luminescent red dye Eosin B, was found to enhance adherence and visualization of the fingerprint on various non-porous as well as adhesive surfaces (Sodhi and Kaur, 2008). QDs, that possess size-dependent fluorescence around twenty times brighter than luminescent dyes, have also been used for fingermark detection. Both QD nanocomposite dispersions, as well as QD powders, exhibit promising results for latent fingerprint detection.
Thus, nanotechnology based techniques are gaining impetus in forensics investigation. These technologies can not only be used for enhancing the existing procedures but also represent novel techniques for detection and identification. The nanoscale detecting devices such as TEM/SEM/AFM and microfluidic devices can be used to detect and analyze very minute quantities of evidence thus increasing the sensitivity of the procedure. At the same time, the use of nanomaterials in currency notes, inks, passports and credit cards can increase the security and ease of detection.
