Development of a Surface-Enhanced Raman Spectroscopy Method for the Detection of Benzodiazepines in Urine

Benzodiazepines are among the most prescribed compounds for anti-anxiety and are present in many toxicological screens. These drugs are also prominent in the commission of drug facilitated sexual assaults due their effects on the central nervous system. Due to their potency, a low dose of these compounds is often administered to victims; therefore, the target detection limit for these compounds in biological samples is 10 ng/mL. Currently these compounds are predominantly analyzed using immunoassay techniques; however more specific screening methods are needed. The goal of this dissertation was to develop a rapid, specific screening technique for benzodiazepines in urine samples utilizing surface-enhanced Raman spectroscopy (SERS), which has previously been shown be capable of to detect trace quantities of pharmaceutical compounds in aqueous solutions. Surface enhanced Raman spectroscopy has the advantage of overcoming the low sensitivity and fluorescence effects seen with conventional Raman spectroscopy. The spectra are obtained by applying an analyte onto a SERS-active metal substrate such as colloidal metal particles. SERS signals can be further increased with the addition of aggregate solutions. These agents cause the nanoparticles to amass and form hot-spots which increase the signal intensity. In this work, the colloidal particles are spherical gold nanoparticles in aqueous solution with an average size of approximately 30 nm. The optimum aggregating agent for the detection of benzodiazepines was determined to be 16.7 mM MgCl2, providing the highest signal intensities at the lowest drug concentrations with limits of detection between 0.5 and 127 ng/mL. A supported liquid extraction technique was utilized as a rapid clean extraction for benzodiazepines from urine at a pH of 5.0, allowing for clean extraction with limits of detection between 6 and 640 ng/mL. It was shown that at this pH other drugs that are prevalent in urine samples can be removed providing the selective detection of the benzodiazepine of interest. This technique has been shown to provide rapid (less than twenty minutes), sensitive, and specific detection of benzodiazepines at low concentrations in urine. It provides the forensic community with a sensitive and specific screening technique for the detection of benzodiazepines in drug facilitated assault cases.

Graphene quantum dots and Nafion composite as an ultrasensitive electrochemical sensor for the detection of dopamine

A novel electrochemical sensor for highly sensitive and selective detection of dopamine (DA) was developed based on a graphene quantum dots (GQDs) and Nafion composite modified glassy carbon electrode (GCE). GQDs were synthesized by a hydrothermal approach for cutting graphene sheets into GQDs and characterized by TEM, UV-vis, photoluminescence, and FT-IR spectra. The GQDs had carboxyl groups with a negative charge, which not only provided good stability, but also enabled interaction with amine functional groups in DA through electrostatic interaction to enhance the specificity of DA. The interaction and electron communication between GQDs and DA can be further strengthened via π-π stacking force. Nafion was used as an anchoring agent to increase the robustness of GQDs on the electrode surface and sensor stability and reproducibility. The GQDs-Nafion composite exhibits a good linear range of 5 nM to 100 μM and a limit of detection as low as 0.45 nM in the detection of DA. The proposed electrochemical sensor also displays good selectivity and high stability and could be used for the determination of DA in real samples with satisfactory results. The present study provides a powerful avenue for the design of an ultrasensitive detection method for clinical application.

Ozone-induced dissociation of conjugated lipids reveals significant reaction rate enhancements and characteristic odd-electron product ions

Ozone-induced dissociation (OzID) is an alternative ion activation method that relies on the gas phase ion-molecule reaction between a mass-selected target ion and ozone in an ion trap mass spectrometer. Herein, we evaluated the performance of OzID for both the structural elucidation and selective detection of conjugated carbon-carbon double bond motifs within lipids. The relative reactivity trends for \[M + X](+) ions (where X = Li, Na, K) formed via electrospray ionization (ESI) of conjugated versus nonconjugated fatty acid methyl esters (FAMEs) were examined using two different OzID-enabled linear ion-trap mass spectrometers. Compared with nonconjugated analogues, FAMEs derived from conjugated linoleic acids were found to react up to 200 times faster and to yield characteristic radical cations. The significantly enhanced reactivity of conjugated isomers means that OzID product ions can be observed without invoking a reaction delay in the experimental sequence (i.e., trapping of ions in the presence of ozone is not required). This possibility has been exploited to undertake neutral-loss scans on a triple quadrupole mass spectrometer targeting characteristic OzID transitions. Such analyses reveal the presence of conjugated double bonds in lipids extracted from selected foodstuffs. Finally, by benchmarking of the absolute ozone concentration inside the ion trap, second order rate constants for the gas phase reactions between unsaturated organic ions and ozone were obtained. These results demonstrate a significant influence of the adducting metal on reaction rate constants in the fashion Li > Na > K.

Fabrication of optochemical and electrochemical sensors using thin films of porphyrin and phthalocyanine derivatives

This paper describes the fabrication of thin films of porphyrin and metallophthalocyanine derivatives on different substrates for the optochemical detection of HCl gas and electrochemical determination of L-cysteine (CySH). Solid state gas sensor for HCl gas was fabricated by coating meso-substituted porphyrin derivatives on glass slide and examined optochemical sensing of HCl gas. The concentration of gaseous HCl was monitored from the changes in the absorbance of Soret band. Among the different porphyrin derivatives, meso- tetramesitylporphyrin (MTMP) coated film showed excellent sensitivity towards HCl and achieved a detection limit of 0.03ppm HCl. Further, we have studied the self-assembly of 1,8,15,22-tetraaminometallophthalocyanine (4α-MTAPc; M = Co and Ni) from DMF on GC electrode. The CVs for the self-assembled monolayers (SAMs) of 4α-CoIITAPc and 4α-NiIITAPc show two pairs of well-defined redox couple corresponding to metal and ring. Using the 4α-CoIITAPc SAM modified electrode, sensitive and selective detection of L-cysteine was demonstrated. Further, the SAM modified electrode also successfully separates the oxidation potentials of AA and CySH with a peak separation of 320mV.

Direct estimation of an element of order matrix from H-1 NMR spectra of strongly dipolar coupled spins

NMR spectra of molecules oriented in thermotropic liquid crystalline media provide information on the molecular structure and order. The spins are generally strongly dipolar coupled and the spectral analyse require the tedious and time consuming numerical iterative calculations. The present study demonstrates the application of multiple quantum spin state selective detection of single quantum transitions for mimicking the homonuclear decoupling and the direct estimation of an element of ordering matrix. This information is utilized to estimate the nearly accurate starting dipolar couplings for iterative calculations. The studies on the spectra of strongly dipolar coupled five and six interacting spin systems are reported.

Proton NMR studies of dihalogenated phenyl benzamides: two-dimensional higher quantum methodologies

The scalar coupled proton NMR spectra of many organic molecules possessing more than one phenyl ring are generally complex due to degeneracy of transitions arising from the closely resonating protons, in addition to several short- and long- range couplings experienced by each proton. Analogous situations are generally encountered in derivatives of halogenated benzanilides. Extraction of information from such spectra is challenging and demands the differentiation of spectrum pertaining to each phenyl ring and the simplification of their spectral complexity. The present study employs the blend of independent spin system filtering and the spin-state selective detection of single quantum (SO) transitions by the two-dimensional multiple quantum (MQ) methodology in achieving this goal. The precise values of the scalar couplings of very small magnitudes have been derived by double quantum resolved experiments. The experiments also provide the relative signs of heteronuclear couplings. Studies on four isomers of dilhalogenated benzanilides are reported in this work.

Nickel substitution induced effects on gas sensing properties of cobalt ferrite nanoparticles

Ni2+ ion induced unusual conductivity reversal and an enhancement in the gas sensing properties of ferrites based gas sensors, is reported. The Co1-xNixFe2O4 (for x = 0, 0.5 and 1) nanoparticles were synthesized by wet chemical co-precipitation method and gas sensing properties were studied as a function of composition and temperature. The structural, morphological and microstructural characterization revealed crystallite size of in the range 10-20 nm with porous morphology consisting of nano-sized grains. The Energy Dispersive X-ray (EDX) mapping confirms homogeneous distribution of Co, Ni, Fe and O elements in the ferrites. The non-stoichiometry of the inverse spinel type ferrites and the relative concentration of Ni3+/Co3+ defects were studied using X-ray photoelectron spectroscopy. It is found that the addition of Ni2+ ions into cobalt ferrite shows preferred selectivity towards CO gas at high temperature (325 degrees C) and ethanol gas at low temperature (250 degrees C), unlike undoped cobalt ferrite or undoped nickel ferrite, which show similar response for both these gases. Moreover, an unusual conductivity reversal is observed, except cobalt ferrite due to the difference in reactivity of the gases as well as characteristic non-stoichiometry of ferrites. This behavior is highly gas ambient dependent and hence can be well-exploited for selective detection of gases. (C) 2015 Elsevier B.V. All rights reserved.

A novel, sensitive potentiometric hydrocarbon sensor for high-vacuum applications.

A potentiometric device based on interfacing a solid electrolyte oxygen ion conductor with a thin platinum film acts as a robust, reproducible sensor for the detection of hydrocarbons in high- or ultrahigh-vacuum environments. Sensitivities in the order of approximately 5 x 10(-10) mbar are achievable under open circuit conditions, with good selectivity for discrimination between n-butane on one hand and toluene, n-octane, n-hexane, and 1-butene on the other hand. The sensor's sensitivity may be tuned by operating under constant current (closed circuit) conditions; injection of anodic current is also a very effective means of restoring a clean sensing surface at any desired point. XPS data and potentiometric measurements confirm the proposed mode of sensing action: the steady-state coverage of Oa, which sets the potential of the Pt sensing electrode, is determined by the partial pressure and dissociative sticking probability of the impinging hydrocarbon. The principles established here provide the basis for a viable, inherently flexible, and promising means for the sensitive and selective detection of hydrocarbons under demanding conditions.

Turn-on fluorescent cyanide sensor based on copper ion-modified CdTe quantum dots

A new fluorescent sensor for the sensitive and selective detection of cyanide (CN-) in aqueous media was developed herein. The sensing approach is based on CN--modulated quenching behavior of Cu2+ toward the photoluminescence (PL) of CdTe quantum dots (QDs). In the presence of CN-, the PL of QDs that have been quenched by Cu2+ was found to be efficiently recovered, which then allows the detection of CN- in a very simple approach. Experimental results showed that the pH of the buffer solution, concentration of copper ions, and size of CdTe QDs all influenced the response of the sensor to CN-. Under the optimal conditions, a good linear relationship between the PL intensity and the concentration of CN- can be obtained in the range of 3.0 x 10(-7) to 1.2 x 10(-5) M, with a detection limit as low as 1.5 x 10(-7) M. In addition, the present fluorescent sensor possesses remarkable selectivity for cyanide over other anions, and negligible influences were observed on the cyanide detection by the coexistence of other anions or biological species (such as albumin and typical blood constituents).

Effects of heteropoly acids and surfactant on electrochemiluminescence of tris(2,2 '-bipyridine) ruthenium(II)

The effects of heteropoly acids and Triton X-100 on electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) are investigated. Triton X-100 prevents the oxidation of oxalate and results in an increase of the ECL signal. H5SiW11VO40 prevents the direct oxidation of oxalate and makes the electrochemical behavior of Ru(bpy)(3)(2+) less reversible, which leads to a decrease of the ECL signal. In contrast, H3PMo12O40 has negligible effect on ECL intensity. Some possible reasons for the effects on the ECL of Ru(bpy)(3)(2+) are discussed based on the adsorption of SiW11VO405- on electrode surface and the ion association between SiW11VO405- and Ru(bpy)(3)(2+). The signal of ECL decreases linearly with the concentration of heteropoly acid in the range from 2x10-6 to 1x10(-4) mol l(-1). The results indicate that ECL of RU(bpy)(3)(2+) is a potential sensitive and selective detection method for heteropoly acids and hence for the elements comprised in them.

Cadmium Selenide Based Core-Shell Quantum Dots for Biosensing and Imaging Applications

The overall focus of the thesis involves the synthesis and characterization of CdSe QDs overcoated with shell materials for various biological and chemical sensing applications. Second chapter deals with the synthesis and characterization of CdSe and CdSe/ZnS core shell QDs. The primary attention of this work is to develop a simple method based on photoinduced charge transfer to optimize the shell thickness. Synthesis of water soluble CdSe QDs, their cytotoxicity analysis and investigation of nonlinear optical properties form the subject of third chapter. Final chapter deals with development of QD based sensor systems for the selective detection of biologically and environmentally important analytes from aqueous media.

Rapid qualitative and quantitative analysis of proanthocyanidin oligomers and polymers by UPLC-MS/MS.

This paper presents the development of a rapid method with ultraperformance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) for the qualitative and quantitative analyses of plant proanthocyanidins directly from crude plant extracts. The method utilizes a range of cone voltages to achieve the depolymerization step in the ion source of both smaller oligomers and larger polymers. The formed depolymerization products are further fragmented in the collision cell to enable their selective detection. This UPLC-MS/MS method is able to separately quantitate the terminal and extension units of the most common proanthocyanidin subclasses, that is, procyanidins and prodelphinidins. The resulting data enable (1) quantitation of the total proanthocyanidin content, (2) quantitation of total procyanidins and prodelphinidins including the procyanidin/prodelphinidin ratio, (3) estimation of the mean degree of polymerization for the oligomers and polymers, and (4) estimation of how the different procyanidin and prodelphinidin types are distributed along the chromatographic hump typically produced by large proanthocyanidins. All of this is achieved within the 10 min period of analysis, which makes the presented method a significant addition to the chemistry tools currently available for the qualitative and quantitative analyses of complex proanthocyanidin mixtures from plant extracts.

On the pH dependence of electroactivity of poly(methylene blue) films

The electrochemical behavior of poly(methylene blue) on different electrodes has been investigated by electrochemical quartz crystal microbalance and in situ spectrophotometric measurements coupled to cyclic voltammetry. Polymeric films were obtained potentiodynamically and the charge transport mechanism was analyzed. The electrochemical results show that polymer electroactivity depends not only on pH but also on the substrate. Charge compensation changes with both pH and the size of the anions showing a transition in the pH range of polymer pKa. It was demonstrated by spectroelectrochemical experiments that the electroactivity of the film depends on the radical/radical cation equilibrium. The potentials where the most electroactive species are formed have been determined. (C) 2009 Elsevier Ltd. All rights reserved.

Graphene nanodots-encaged porous gold electrode fabricated via ion beam sputtering deposition for electrochemical analysis of heavy metal ions

All rights reserved. A graphene nanodots-encaged porous gold electrode via ion beam sputtering deposition (IBSD) for electrochemical sensing is presented. The electrodes were fabricated using Au target, and a composite target of Al and graphene, which were simultaneously sputtered onto glass substrates by Ar ion beam, followed with hydrochloric acid corrosion. The as-prepared graphene nanodots-encaged porous gold electrodes were then used for the analysis of heavy metal ions, e.g. Cu2+ and Pb2+ by Osteryoung square wave voltammetry (OSWV). These porous electrodes exhibited enhanced detection range for the heavy metal ions due to the entrapped graphene nanodots in 3-D porous structure. In addition, it was also found that when the thickness of porous electrode reached 40 nm the detection sensitivity came into saturation. The linear detection range is 0.009-4 μM for Cu2+ and 0.006-2.5 μM for Pb2+. Good reusability and repeatability were also observed. The formation mechanism and 3-D structure of the porous electrode were also investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectra (XPS). This graphene entrapped 3-D porous structure may envision promising applications in sensing devices.

Simple and signal-off electrochemical biosensor for mercury(II) based on thymine-mercury-thymine hybridization directly on graphene

Abstract A simple, signal-off and reusable electrochemical biosensor was developed for sensitive and selective detection of mercury(II) based on thymine-mercury(II)-thymine (T-Hg²⁺-T) complex and the remarkable difference in the affinity of graphene with double strand DNA (ds-DNA) and single strand DNA (ss-DNA). Our system was composed of ferrocene-tagged probe DNA and graphene. Due to the noncovalent assembly, the ferrocene-tagged probe ss-DNA was immobilized on the surface of graphene nanosheets directly and employed to amplify the electrochemical signal. In the presence of Hg²⁺, the ferrocene-labeled T-rich DNA probe hybridized with target probe to form ds-DNA via the Hg²⁺-mediated coordination of T-Hg²⁺-T base pairs. As a result, the duplex DNA complex kept away from the graphene surface due to the weak affinity of graphene and ds-DNA, and the redox current decreased substantially. Meanwhile, the graphene decorated GCE surface was released for the reusability. Under the optimal conditions, the proposed sensor showed a linear concentration range from 25 pM to 10 μM with a detection limit of 5 pM for Hg²⁺ detection. The strategy afforded exquisite selectivity for Hg²⁺ against other metal ions in real environmental samples.