Time-resolved fluorescence microscopy of gunshot residue: an application to forensic science

Time-resolved fluorescence microscopy has rapidly emerged as the technique of choice for many researchers aiming to gain specific insights into the dynamics of intricate biological systems. Although the unique advantages the technique provides over other methods have proven to be particularly useful in the biosciences, to date they have been largely unexploited by other research disciplines. In this paper, we demonstrate the capacity of time-resolved fluorescence microscopy as a practical analytical tool in the forensic sciences via the imaging of gunshot residues that are expelled when a firearm is discharged. This information may prove to be useful for determination of the true sequence of events that took place in a firearm related crime.

Development of a new versatile computer controlled electrochemical/ESR data acquisition system

A new versatile computer controlled electrochemlcal/ESR data acquisition system has been developed for the Investigation of short-lived radicals with life-times of 20 milliseconds and greater, Different computer programs have been developed to monitor the decay of radicals; over hours or minutes, seconds or milliseconds. Signal averaging and Fourier smoothing is employed in order to improve the signal to noise ratio. Two microcomputers are used to control the system, one home-made computer containing the M6800 chip which controls the magnetic field, and an IBM PC XT which controls the electrochemistry and the data acquisition. The computer programs are written in Fortran and C, and call machine language subroutines, The system functions by having the radical generated by an electrochemical pulse: after or during the pulse the ESR data are collected. Decaying radicals which have half-lives of seconds or greater have their spectra collected in the magnetic field domain, which can be swept as fast as 200 Gauss per second. The decay of the radicals in the millisecond region is monitored by time-resolved ESR: a technique in which data is collected in both the time domain and in the magnetic field domain. Previously, time-resolved ESR has been used (without field modulation) to investigate ultra-short-lived species with life-times in the region of only a few microseconds. The application of the data acquisition system to chemical systems is illustrated. This is the first time a computer controlled system whereby the radical is generated by electrochemical means and subsequently the ESR data collected, has been developed.

Kinetic effects of halide ions on the morphological evolution of silver nanoplates

Time-resolved extinction spectroscopy is employed to study the reaction kinetics in the shape-conversion reaction involving halide ions (including Cl-, Br- and I-) etching (sculpturing) silver nanoplates. A series of time-resolved extinction spectra are obtained during the in situ etching process and the evolution of surface plasmon resonance (SPR) of the silver nanoparticles is analyzed. Spectral analysis indicates that the conversion of nanoprisms starts simultaneously with the emergence of nanodisks when the halide ions are added. The etching rate of different halide ions is evaluated through the in-plane dipole resonance peak intensity of silver nanoplates vs. the reaction time (dI/dt). The relationship between the etching rate and the halide ion concentration shows that the halide ion etching reaction can be considered as a pseudo-first-order reaction. The effect of different halide ions on the shape-conversion of silver nanoplates is compared in detail. The activation energy of the etching reaction is calculated, which indicates that the etching ability of different halide ions is on the order of Cl - < I- < Br-.

Two-dimensional correlation localized surface plasmon resonance spectroscopy for analysis of the interaction between metal nanoparticles and bovine serum albumin

Time-resolved extinction spectra assisted with two-dimensional correlation spectroscopy (2DCOS) analysis and principal component analysis (PCA) were employed to investigate the interaction between bovine serum albumin (BSA) and metal nanoparticles (NPs). A series of localized surface plasmon resonance (LSPR) spectra of metal NPs were measured just after a small amount of BSA was added into metal colloids. Through 2DCOS analysis, remarkable changes in the intensities of the LSPR were observed. The interaction process was totally divided into three periods according to the PCA. Transmission electron microscopy, dynamic light scattering, and ζ-potential measurements were also employed to characterize the interaction between BSA and metal NPs. The addition of BSA brings silver NPs to aggregate through the electrostatic interaction between them, but it has less effect on gold NPs. In a gold and silver mixed system, gold NPs can affect the interaction of silver NPs and BSA, leading it to weaken. The combination of 2DCOS analysis and LSPR spectroscopy is powerful for exploring the LSPR spectra of the metal NP involved systems. This combined technique holds great potential in LSPR sensing through analysis of slight, slim spectral changes of metal colloids

Direct observation of the intergallery expansion of polystyrene–montmorillonite nanocomposites

The intergallery expansion development of a series of differently modified montmorillonite polystyrene nanocomposites was directly observed with time-resolved in situ small-angle X-ray scattering (SAXS) using synchrotron radiation. The results indicated that the interlayer expansion varied depending on the clay modification and the chemical compatibility of the clay modifiers with the styrene monomer. The influence of the differently modified clays on the free radical polymerization was also investigated, particularly the effect on the conversion of styrene and molecular weight evolution of the polymer. On the basis of the kinetic study of the polymerization of styrene in the presence of varied modified clay particles, the intergallery expansion mechanism was postulated and discussed for different composite morphologies. Such studies provide an important guideline for the design of clay modifiers and development of clay–polymer nanocomposites.

A new insight into growth mechanism and kinetics of mesoporous silica nanoparticles by in situ small angle x-ray scattering

The growth mechanism and kinetics of mesoporous silica nanoparticles (MSNs) were investigated for the first time by using a synchrotron time-resolved small-angle X-ray scattering (SAXS) analysis. The synchrotron SAXS offers unsurpassed time resolution and the ability to detect structural changes of nanometer sized objects, which are beneficial for the understanding of the growth mechanism of small MSNs (∼20 nm). The Porod invariant was used to quantify the conversion of tetraethyl orthosilicate (TEOS) in silica during MSN formation, and the growth kinetics were investigated at different solution pH and temperature through calculating the scattering invariant as a function of reaction time. The growth of MSNs was found to be accelerated at high temperature and high pH, resulting in a higher rate of silica formation. Modeling SAXS data of micelles, where a well-defined electrostatic interaction is assumed, determines the size and shape of hexadecyltrimethylammonium bromide (CTAB) micelles before and after the addition of TEOS. The results suggested that the micelle size increases and the micelle shape changes from ellipsoid to spherical, which might be attributed to the solubilization of TEOS in the hydrophobic core of CTAB micelles. A new "swelling-shrinking" mechanism is proposed. The mechanism provides new insights into understanding MSN growth for the formation of functional mesoporous materials exhibiting controlled morphologies. The SAXS analyses were correlated to the structure of CTAB micelles and chemical reaction of TEOS. This study has provided critical information to an understanding of the growth kinetics and mechanism of MSNs.

Facile synthesis of silver submicrospheres and their applications

Uniform silver submicrospheres were synthesized under ambient conditions, through reduction of silver nitrate using ascorbic acid as a reducing agent and Tween 20 as a stabilizer. The silver submicroparticles exhibited strong catalytic activity for the reduction of 4-nitrophenol by sodium borohydride (NaBH4). Significantly, the aggregates of a few silver submicroparticles can be used as surface-enhanced Raman scattering (SERS) substrate to improve markedly the Raman signal of crystal violet. The morphologies of silver submicroparticles can be controlled by changing reaction conditions. The formation process of silver submicroparticles was monitored by time-resolved extinction spectroscopy. The influences of concentrations and molar ratios of reaction reagents on the formation of silver submicroparticles are discussed.

Peptide sequence effects control the single pot reduction, nucleation, and growth of Au nanoparticles

Peptides have demonstrated unique capabilities to fabricate inorganic nanomaterials of numerous compositions through noncovalent binding of the growing surface in solution. In this contribution, we demonstrate that these biomolecules can control all facets of Au nanoparticle fabrication, including Au3+ reduction, without the use of secondary reagents. In this regard using the AuBP1 peptide, the N-terminal tryptophan residue is responsible for driving Au3+ reduction to generate Au nanoparticles passivated by the oxidized peptide in solution, where localized residue context effects control the reducing strength of the biomolecule. The process was fully monitored by both time-resolved monitoring of the growth of the localized surface plasmon resonance and transmission electron microscopy. Nanoparticle growth occurs by a unique disaggregation of nanoparticle aggregates in solution. Computational modeling demonstrated that the oxidized residue of the peptide sequence does not impact the biomolecule's ability to bind the inorganic surface, as compared to the parent peptide, confirming that the biomolecule can be exploited for all steps in the nanoparticle fabrication process. Overall, these results expand the utility of peptides for the fabrication of inorganic nanomaterials, more strongly mimicking their use in nature via biomineralization processes. Furthermore, these capabilities enhance the simplicity of nanoparticle production and could find rapid use in the generation of complex multicomponent materials or nanoparticle assembly.

Internal representation of movement in children with developmental coordination disorder : a mental rotation task

Recent studies show that children with developmental coordination disorder (DCD) have difficulties in generating an accurate visuospatial representation of an intended action, which are shown by deficits in motor imagery. This study sought to test this hypothesis further using a mental rotation paradigm. It was predicted that children with DCD would not conform to the typical pattern of responding when required to imagine movement of their limbs. Participants included 16 children with DCD and 18 control children; mean age for the DCD group was 10 years 4 months, and for controls 10 years. The task required children to judge the handedness of single-hand images that were presented at angles between 0° and 180° at 45° intervals in either direction. Results were broadly consistent with the hypothesis above. Responses of the control children conformed to the typical pattern of mental rotation: a moderate trade-off between response time and angle of rotation. The response pattern for the DCD group was less typical, with a small trade-off function. Response accuracy did not differ between groups. It was suggested that children with DCD, unlike controls, do not automatically enlist motor imagery when performing mental rotation, but rely on an alternative object-based strategy that preserves speed and accuracy. This occurs because these children manifest a reduced ability to make imagined transformations from an egocentric or first-person perspective.

The addition of a surfactant at regular time intervals in the mechanical alloying process

The impact of regular additions of a surfactant (ethylene bis-stearamide; EBS) at different time intervals was investigated on the powder characteristics of a biomedical Ti-10Nb-3Mo alloy (wt.%). Ball milling was performed for 10 h on the elemental powders in four series of experiments at two rotation speeds (200 and 300 rpm). The addition of 2 wt.% total EBS at different time intervals during ball milling resulted in noticeable changes in particle size and morphology of the powders. The surfactant addition at shorter time intervals led to the formation of finer particles, a more homogenous powder distribution, a higher powder yield, and a lower contamination content in the final materials. Thermal analysis of the powders after ball milling suggested that differing decomposition rates of the surfactant were responsible for the measured powder particle changes and contamination contents. The results also indicated that the addition of surfactant during ball milling at 200 rpm caused a delay in the alloy formation, whereas ball milling at 300 rpm favored the formation of the titanium alloy.Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.