Forensic examination of plastic drinking straws based on their physical characteristics and manufacturing marks.

This work highlights the evidential value of examining plastic drinking straws to establish linkages between multiple sources for forensic intelligence, investigative or prosecution purposes. Plastic drinking straws are commonly encountered in drug cases, either as inhalational paraphernalia or as packaging material. However, to the best of our knowledge, systematic studies on the evidential value of straws have not previously been carried out. In this study, over 80 packets of clear and colourless straws-most of which were visually similar-were purchased from various commercial outlets in Singapore. Some physical characteristics (viz., polarizing patterns, thickness, circumference and mass per unit length) and the manufacturing marks of these straws were examined to assess their potentials for discriminating straws from different packets. Comparison of polarizing patterns yielded a discrimination of approximately 69%, while thickness, circumference, and mass per unit length measurements resulted in lower discriminations. Comparison microscopy of manufacturing marks was found to be the most discriminating among all techniques employed herein, with a discrimination of about 95%, even among straws with similar polarizing patterns.

Snap-lock bags with red band: A study of manufacturing characteristics, thermal and chemical properties.

Drug packaging is commonly submitted to the Forensic Chemistry and Physics Laboratory of the Health Sciences Authority, Singapore, for examination. The drugs seized are often packaged in plastic bags. These bags are examined for linkages to provide law enforcement with useful associations between the traffickers and drug abusers. The plastic bags submitted may include snap-lock bags, some with a red band located above the snap-lock closure and some without. Current techniques for examination involve looking at the physical characteristics (dimensions, thickness and polarising patterns) and manufacturing marks of these bags. In cases where manufacturing marks on the main body of the bags are poor or absent, the manufacturing characteristics present on the red band can be examined. A study involving approximately 1000 bags was conducted to better understand the variations in the manufacturing characteristics of the red band. This understanding is crucial in helping to determine associations/eliminations between bags. Two instrumental techniques, namely differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) were explored to evaluate the effectiveness of examining the chemical composition to discriminate the bags.

New approach for multilayered microstructures fabrication based on a water-soluble backing substrate.

We demonstrate a new approach for woodpile microstructure fabrication. The method involves the use of polyvinyl alcohol (PVA) as a sacrificial substrate for the transfer of SU-8 films to prepatterned structures. The surface activated PVA substrate allows good wettability of SU-8 film and its solubility in water eliminates the need of delaminating SU-8 structures from the substrate. This makes the fabrication process much simplified and we successfully demonstrate eight-layer stacking of gratings. Fourier transform infrared spectra of single-layer and four-layer grating structures show a broader transmission dip spectrum compared to their film counterparts, indicating their potential use as broadband terahertz (THz) absorbers.

Design of single peptides for self-assembled conduction channels.

Self-assembly of peptides provides the possibility of achieving relatively long range order on surfaces. These ordered peptides can also form channels that can be used as conduction channels. In the past, studies were focused on electron conduction through the secondary structure and amine bond of peptides and these restrict conduction of electrons over a short range (a few nanometers). In this work, we demonstrate the realization of electron conduction over a longer range of a few hundred nanometers via π-π stacking of the phenyl groups in the tyrosine residue of a single peptide. The peptide used in this work was designed with a phenyl ring for π-π stacking at one end and a carboxylic group at the other end for binding to aminopropyltriethoxysilane (APTES) treated silicon wafer. The distance between the peptides is controlled by a disulfide bond formed between neighboring cysteine residue and also by the amine groups of aminopropyltriethoxysilane. We demonstrate that the self-assembled peptide is conducting in the dry state over hundreds of nanometers, realizing the possibility of using peptide as a molecular wire.