Hilton Kobus

Cadmium sulfide quantum dot/chitosan nanocomposites for latent fingermark detection.

The detection of latent fingermarks is a challenging task in forensic science. Here we present work using highly photoluminescent cadmium sulfide (CdS) quantum dots (QDs) encapsulated in an inexpensive biopolymeric chitosan matrix for latent fingermark detection. Cadmium ions were chelated within the chitosan matrix followed by the rapid addition of sodium sulfide to produce a CdS/chitosan nanocomposite. The average QD size was investigated as a function of precursor concentrations using ultra-violet-vis (UV-vis) spectrophotometry and the QDs were imaged with transmission electron microscopy (TEM). Fluorescence spectrophotometry of the QDs at an excitation of 450 nm showed a narrow emission at 531 nm and broad emission between 600 and 850 nm with a maximum at 716 nm. Freshly deposited latent fingermarks deposited on aluminium foil were clearly detected under a Rofin Polilight at 450 nm by dusting with a freeze-dried suspension of the CdS/chitosan nanocomposite and a surfactant, tergitol, giving a so-called quantum dot surfactant (QDS) powder.

Surface-assisted laser desorption ionization mass spectrometry techniques for application in forensics

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is an excellent analytical technique for the rapid and sensitive analysis of macromolecules (>700 Da), such as peptides, proteins, nucleic acids, and synthetic polymers. However, the detection of smaller organic molecules with masses below 700 Da using MALDI-MS is challenging due to the appearance of matrix adducts and matrix fragment peaks in the same spectral range. Recently, nanostructured substrates have been developed that facilitate matrix-free laser desorption ionization (LDI), contributing to an emerging analytical paradigm referred to as surface-assisted laser desorption ionization (SALDI) MS. Since SALDI enables the detection of small organic molecules, it is rapidly growing in popularity, including in the field of forensics. At the same time, SALDI also holds significant potential as a high throughput analytical tool in roadside, work place and athlete drug testing. In this review, we discuss recent advances in SALDI techniques such as desorption ionization on porous silicon (DIOS), nano-initiator mass spectrometry (NIMS) and nano assisted laser desorption ionization (NALDI™) and compare their strengths and weaknesses with particular focus on forensic applications. These include the detection of illicit drug molecules and their metabolites in biological matrices and small molecule detection from forensic samples including banknotes and fingerprints. Finally, the review highlights recent advances in mass spectrometry imaging (MSI) using SALDI techniques.

Improving the Effectiveness of Fluorescence for the Detection of Semen Stains on Fabrics

The paper describes the use of the Polilight, a light source based on a xenon arc lamp, to exploit the fluorescence properties of semen as an aid to searching fabrics for stains in sexual assault cases. The broad excitation spectrum of semen allows the fluorescence to be generated at a range of wavelengths. This permits the excitation and emission conditions to be selected that minimize interference from background fluorescence of the fabric and thereby optimizes the contrast between the fabric and the stain. A common method for the observation of fluorescence is the use of colored plastic goggles or filters. The paper shows that the detection of fluorescence from semen stains is significantly enhanced using appropriate interference filters.

THE ANALYSIS OF SMALL GLASS FRAGMENTS USING INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

Inductively coupled plasma mass spectrometry using solution nebulization has the ability to analyze up to 70 elements with good precision, accuracy, and sensitivity and is, therefore, well suited for the trace element analysis of glass. However, the technique places severe restrictions on sample preparation. High concentrations of acids or dissolved solids, changes in sample viscosity and molecular compound formation can cause physical, spectral and chemical interference. Solubilization of the glass samples based on a three acid digestion procedure (HF, HNO3, HCl 2:1:1) has been found to minimize these problems. Up to 62 elements have been determined in a range of glass samples. Glasses that could not be distinguished on the basis of refractive index measurement could be discriminated. A procedure of measuring a range of elemental ratios, which eliminated the need for weighing, was used to compare small samples typical of casework.

Rapid detection of illicit drugs in neat saliva using desorption/ionization on porous silicon

The ability to detect illicit drugs directly in oral fluids is of major interest for roadside, workplace and athlete drug testing. For example, roadside testing for popular drugs of abuse is being rolled out by law enforcement agencies following the introduction of legislation in several countries all over the world. This paper reports on the direct analysis of methamphetamine, cocaine and 3,4-methylenedioxymethamphetamine in oral fluids using a hydrophobic porous silicon array as a combined drug extraction and concentration medium. Analysis by laser desorption/ionization time-of-flight mass spectrometry (MS) identified these drugs with a sensitivity in line with the suggested confirmatory cut-off concentrations, and 300 times faster. In addition, MS imaging demonstrated good spot-to-spot reproducibility of the signal. Our analytical approach is compatible with multiplexing and is therefore suitable for high-throughput analysis of samples obtained from drug testing in the field. Furthermore, the application of this analytical technology is not limited to illicit drugs or oral fluids. Indeed, we believe that this platform technology could be applied to the high-throughput analysis of diverse metabolites in body fluids.

Evaluation of X-ray microfluorescence spectrometry for the elemental analysis of firearm discharge residues

Abstract The conventional technique employed to sample Firearm Discharge Residues (FDRs) is by pressing an adhesive coated SEM stub repeatedly over the area of interest. The sample is then analysed by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDX). While having excellent spatial resolution, the SEM/EDX process lacks elemental sensitivity compared to other techniques such as X-ray fluorescence (XRF), where 100× to 1000× better elemental sensitivity may be achieved. The aim of this preliminary study was to evaluate relatively new technology, X-ray microfluorescence (micro-XRF), as a method of analysing FDRs, to compare the ability of micro-XRF to screen for FDR particles on SEM stubs with that of conventional SEM/EDX analysis, and to evaluate the ability of the micro-XRF to conduct on-target FDR analysis. The micro-XRF utilises a non-destructive method that can rapidly locate and analyse individual FDR particles 10 μm in diameter and larger. This analysis has the advantage that it can produce elemental maps (by X-ray mapping) directly from the target substrates, indicating the distribution of elements across a sample. Different types of ammunition were employed to include various types of primer and bullet compositions. The projectiles and primers were fired onto various target substrates at close-range and the residues analysed by micro-XRF. SEM stubs known to contain FDR particles were also analysed by micro-XRF. The results indicate that micro-XRF can effectively detect and analyse FDR particles that are larger than 10 μm in diameter. With the present instrumental configuration (50 W tube and 100 μm collimator) the micro-XRF cannot replace the SEM/EDX for the analysis of individual FDR particles less than 10 μm in diameter. It was demonstrated that micro-XRF has significant advantages for the on-target analysis of residues resulting from close range discharges (less than 30 cm). Information obtained from the micro-XRF analysis of the bullet wipe area can also give an indication of projectile composition.

Improved enhancement of ninhydrin developed fingerprints by cadmium complexation using low temperature photoluminescence techniques.

Fingerprints developed with ninhydrin form stable, colored complexes when treated with various metal salts. Many of these colored complexes can be used to increase the sensitivity of detection of latent prints because of photoluminescent properties. The intensity of this photoluminescence is increased at low temperature (77K), and this is a common characteristic of each of the complexes formed with salts of the IIb group of the Periodic Table. Spectral characteristics of these Group IIb metal complexes and the influence of environmental factors on their formation are reported. These data have helped determine optimal conditions for the enhancement of ninhydrin developed fingerprints. Taking into account spectral characteristics, solubility, versatility, stability, and reproducibility, the use of the cadmium nitrate tetrahydrate complex is advocated for general use for fingerprint enhancement. The use of zinc nitrate is favored if toxicological considerations are paramount, but ninhydrin development has to be carefully controlled if optimal results are to be obtained. Limited applications for mercuric complexes are found when a red shift is desired to remove background effects.

Aptamer sensor for cocaine using minor groove binder based energy transfer.

We report on an optical aptamer sensor for cocaine detection. The cocaine sensitive fluorescein isothiocyanate (FITC)-labeled aptamer underwent a conformational change from a partial single-stranded DNA with a short hairpin to a double-stranded T-junction in the presence of the target. The DNA minor groove binder Hoechst 33342 selectively bound to the double-stranded T-junction, bringing the dye within the Förster radius of FITC, and therefore initiating minor groove binder based energy transfer (MBET), and reporting on the presence of cocaine. The sensor showed a detection limit of 0.2 μM. The sensor was also implemented on a carboxy-functionalized polydimethylsiloxane (PDMS) surface by covalently immobilizing DNA aptamers. The ability of surface-bound cocaine detection is crucial for the development of microfluidic sensors.

Rapid drug detection in oral samples by porous silicon assisted laser desorption/ionization mass spectrometry

The demand for analysis of oral fluid for illicit drugs has arisen with the increased adoption of roadside testing, particularly in countries where changes in legislation allow random roadside testing of drivers for the presence of a palette of illicit drugs such as methamphetamine (MA), 3,4-methylenedioxymethamphetamine (MDMA) and Delta9-tetrahydrocannabinol (THC). Oral samples are currently tested for such drugs at the roadside using an immunoassay-based commercial test kit. Positive roadside tests are sent for confirmatory laboratory analysis, traditionally by means of gas chromatography/mass spectrometry (GC/MS). We present here an alternative rapid analysis technique, porous silicon assisted laser desorption/ionization time-of-flight mass spectrometry (pSi LDI-MS), for the high-throughput analysis of oral fluids. This technique alleviates the need for sample derivatization, requires only sub-microliter sample volumes and allows fast analysis (of the order of seconds). In this study, the application of the technique is demonstrated with real samples from actual roadside testing. The analysis of oral samples resulted in detection of MA and MDMA with no extraction and analysis of THC after ethyl acetate extraction. We propose that, subject to miniaturization of a suitable mass spectrometer, this technique is well suited to underpin the deployment of oral fluid testing in the clinic, workplace and on the roadside.

The analysis of dyes in ball point pen inks on single paper fibres using laser desorption ionisation time of flight mass spectrometry (LDI-TOFMS)

An important requisite for the forensic analysis of inks on documents is that damage to the document is avoided or minimised. This paper describes a technique for dye identification in ballpoint pen inks using LDI-TOFMS on single ink bearing paper fibres and its application to a case. A single ink bearing paper fibre can be prised from the surface of the document under a stereo microscope and presented to the instrument for analysis without further treatment. This sampling process causes imperceptible damage to the surface of the document. Clear mass spectrometric identification of the ink dyes is obtained. A case example is provided to illustrate the practical application of the technique.