Clay-biochar composites for sorptive removal of tetracycline antibiotic in aqueous media.

The focus of this research was to synthesize novel clay-biochar composites by incorporating montmorillonite (MMT) and red earth (RE) clay materials in a municipal solid waste (MSW) biochar for the adsorptive removal of tetracycline (TC) from aqueous media. X-ray Fluorescence Analysis (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Powder X-ray Diffraction (PXRD) and Scanning Electron Microscopy (SEM) were used for the characterization of the synthesized raw biochar (MSW-BC) and clay-biochar composites (MSW-MMT and MSW-RE). Results showed that minute clay particles were dispersed on biochar surfaces. The FTIR bands due to Si-O functional group vibrations in the spectra of the clay-biochar composites provided further evidence for successful composite formation. The kinetic TC adsorption data of MSW-MMT were well fitted to the Elovich model expressing high surface activity of biochar and involvement of multiple mechanisms in the adsorption. The kinetic TC adsorption data of MSW-BC and MSW-RE were fitted to the pseudo second order model indicating dominant contribution of chemisorption mechanism during the adsorption. The adsorption differentiation obtained in the kinetic studies was mainly due to the structure of the combined clay material. The adsorption isotherm data of all the adsorbents were well fitted to the Freundlich model suggesting that the adsorption of TC onto the materials occurred via both physisorption and chemisorption mechanisms. In comparison to the raw biochar and MSW-RE, MSW-MMT exhibited higher TC adsorption capacity. Therefore, MSW-MMT clay-biochar composite could be applied in the remediation of TC antibiotic residues in contaminated aqueous media.

Analysis of enzyme-responsive peptide surfaces by Raman spectroscopy.

We report on the use of Raman spectroscopy as a tool to characterise model peptide functionalised surfaces. By taking advantage of Raman reporters built into the peptide sequence, the enzymatic hydrolysis of these peptides could be determined.

Quantitative characterization of individual microdroplets using surface-enhanced resonance Raman scattering spectroscopy.

Surface-enhanced resonance Raman scattering (SERRS) spectroscopy is a highly sensitive optical technique capable of detecting multiple analytes rapidly and simultaneously. There is significant interest in SERRS detection in micro- and nanotechnologies, as it can be used to detect extremely low analyte concentrations in small volumes of fluids, particularly in microfluidic systems. There is also rapidly growing interest in the field of microdroplets, which promises to offer the analyst many potential advantages over existing technologies for both design and control of microfluidic assays. While there have been rapid advances in both fields in recent years, the literature on SERRS-based detection of individual microdroplets remains lacking. In this paper, we demonstrate the ability to quantitatively detect multiple variable analyte concentrations from within individual microdroplets in real time using SERRS spectroscopy. We also demonstrate the use of a programmable pump control algorithm to generate concentration gradients across a chain of droplets.

Investigation of the stability of labelled nanoparticles for SE(R)RS measurements in cells.

We explore the long-term stability of two different classes of labelled nanoparticles as intracellular SE(R)RS probes. Whilst chemisorbed labels gave stable responses inside cells for extended periods of time, signals from physisorbed labels could only be measured for short periods of time. These results help inform strategies for cellular imaging using vibrational spectroscopies.

SERS mapping of nanoparticle labels in single cells using a microfluidic chip.

We report for the first time the time-resolved mapping of intracellular nanoparticle labels from within living cells retained in a microstructured trap using Raman spectroscopy. The methods employed here also demonstrate the ability to rapidly discriminate between cell populations containing different SERS labels.

Monitoring the uptake and redistribution of metal nanoparticles during cell culture using surface-enhanced Raman scattering spectroscopy.

We describe the uptake of silver nanoparticles by CHO (Chinese hamster ovary) cells and their subsequent fate as a result of cell division during culture, as monitored by surface-enhanced Raman scattering (SERS) spectroscopy. Mapping of populations of cells containing both labeled and native nanoparticles by SERS spectroscopy imaging provided a quantitative method by which the number of intracellular nanoparticles could be monitored. Initially, for a given amount of nanoparticles, the relationship between the number taken up into the cell and the time of incubation was explored. Subsequently, the redistribution of intracellular nanoparticles upon multiple rounds of cell division was investigated. Intracellular SERS signatures remained detectable in the cells for up to four generations, although the abundance and intensity of the signals declined rapidly as nanoparticles were shared with daughter cells. The intensity of the SERS signal was dependent both on stability of the label and their abundance (nanoparticle aggregation increases the extent of the SERS enhancement). The data show that while the labeled nanoparticles remain stable for prolonged periods, during cell division, the changes in signal could be attributed both to a decrease in abundance and distribution (and hence aggregation).

Rapid characterization and quality control of complex cell culture media solutions using raman spectroscopy and chemometrics.

The use of Raman spectroscopy coupled with chemometrics for the rapid identification, characterization, and quality assessment of complex cell culture media components used for industrial mammalian cell culture was investigated. Raman spectroscopy offers significant advantages for the analysis of complex, aqueous-based materials used in biotechnology because there is no need for sample preparation and water is a weak Raman scatterer. We demonstrate the efficacy of the method for the routine analysis of dilute aqueous solution of five different chemically defined (CD) commercial media components used in a Chinese Hamster Ovary (CHO) cell manufacturing process for recombinant proteins.The chemometric processing of the Raman spectral data is the key factor in developing robust methods. Here, we discuss the optimum methods for eliminating baseline drift, background fluctuations, and other instrumentation artifacts to generate reproducible spectral data. Principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) were then employed in the development of a robust routine for both identification and quality evaluation of the five different media components. These methods have the potential to be extremely useful in an industrial context for "in-house" sample handling, tracking, and quality control.

Quantitative surface-enhanced Raman spectroscopy.

The purpose of this tutorial review is to show how surface-enhanced Raman (SERS) and resonance Raman (SERRS) spectroscopy have evolved to the stage where they can be used as a quantitative analytical technique. SER(R)S has enormous potential for a range of applications where high sensitivity needs to be combined with good discrimination between molecular targets, particularly since low cost, compact spectrometers can read the high signal levels that SER(R)S typically provides. These advantages over conventional Raman measurements come at the cost of increased complexity and this review discusses the factors that need to be controlled to generate stable and reproducible SER(R)S calibrations.

Screening tablets for DOB using surface-enhanced Raman spectroscopy.

2,5,-Dimethoxy-4-bromoamphetamine (DOB) is of particular interest among the various "ecstasy" variants because there is an unusually long delay between consumption and effect, which dramatically increases the danger of accidental overdose in users. Screening for DOB in tablets is problematic because it is pharmacologically active at 0.2-3 mg, which is c. 50 times less than 3,4-methylenedioxy-N-methylamphetamine (MDMA) and makes it more difficult to detect in seized tablets using conventional spot tests. The normal Raman spectra of seized DOB tablets are dominated by the bands of the excipient with no evidence of the drug component. Here we report the first use of on-tablet surface-enhanced Raman spectroscopy (SERS) to enhance the signal from a low concentration drug. Raman studies (785-nm excitation) were carried on series of model DOB/lactose tablets (total mass c. 400 mg) containing between 1 mg and 15 microg of DOB and on seized DOB tablets. To generate surface-enhanced spectra, 5 microL of centrifuged silver colloid was dispensed onto the upper surface of the tablets, followed by 5 microL of 1.0 mol/dm(3) NaCl. The probe laser was directed onto the treated area and spectra accumulated for c. 20 sec (10 sec x 2). It was found that the enhancement of the DOB component in the model tablets containing 1 mg DOB/tablet and in the seized tablets tested was so large that their spectra were completely dominated by the vibrational bands of DOB with little or no contribution from the unenhanced lactose excipient. Indeed, the most intense DOB band was visible even in tablets containing just 15 microg of the drug. On-tablet surface-enhanced Raman spectroscopy is a simple method to distinguish between low dose DOB tablets and those with no active constituent. The fact that unique spectra are obtained allows identification of the drug while the lack of sample preparation and short signal accumulation times mean that the entire test can be carried out in <1 min.

Characterization of silicone elastomer vaginal rings containing HIV microbicide TMC120 by Raman spectroscopy.

Silicone elastomer vaginal rings are currently being pursued as a controlled-release strategy for delivering microbicidal substances for the prevention of heterosexual transmission of HIV. Although it is well established that the distribution of drugs in delivery systems influences the release characteristics, in practice the distribution is often difficult to quantify in-situ. Therefore, the aim of this work was to determine whether Raman spectroscopy might provide a rapid, non-contact means of measuring the concentrations of the lead candidate HIV microbicide TMC120 in a silicone elastomer reservoir-type vaginal ring. Vaginal rings loaded with TMC120 were manufactured and sectioned before either Raman mapping an entire ring cross-section (100 microm resolution) or running line scans at appropriate time intervals up to 30 h after manufacture. The results demonstrated that detectable amounts of TMC120, above the silicone elastomer saturation concentration, could be detected up to 1 mm into the sheath, presumably as a consequence of permeation and subsequent reprecipitation. The extent of permeation was found to be similar in rings manufactured at 25 and 80 degrees C.

Surface-enhanced Raman spectroscopy (SERS) for sub-micromolar detection of DNA/RNA mononucleotides.

Surface-enhanced Raman (SER) spectra of all the DNA/RNA mononucleotides have been obtained with high sensitivity using citrate-reduced silver colloids aggregated with MgSO4, rather than the more usual halide ions, which were found to prevent enhancement of these compounds. The SERS spectra of adenine, guanine, thymine, cytosine, and uracil were recorded along with their corresponding nucleosides and 5'-deoxynucleotides. For the cytosine series, all three spectra had similar relative band intensities but the spectra of adenine were different from those of adenosine and dAMP, probably due to differences in orientation on the surface. No enhanced bands from the phosphate or sugar groups were observed. There were general similarities between the SERS spectra of the purine mononucleotides and the pyrimidine mononucleotides, but the spectra were sufficiently different to allow each of them to be distinguished. This method can therefore be used for high sensitivity, label-free identification of mononucleotides.

Quantitative surface-enhanced Raman spectroscopy of dipicolinic acid--towards rapid anthrax endospore detection.

Dipicolinic acid (DPA) is an excellent marker compound for bacterial spores, including those of Bacillus anthracis (anthrax). Surface-enhanced Raman spectroscopy (SERS) potentially has the sensitivity and discrimination needed for trace DPA analysis, but mixing DPA solutions with citrate-reduced silver colloid only yielded measurable SERS spectra at much higher (>80 ppm) concentrations than would be desirable for anthrax detection. Aggregation of the colloid with halide salts eliminated even these small DPA bands but aggregation with Na2SO4(aq) resulted in a remarkable increase in the DPA signals. With sulfate aggregation even 1 ppm solutions gave detectable signals with 10 s accumulation times, which is in the sensitivity range required. Addition of CNS- as an internal standard allowed quantitative DPA analysis, plotting the intensity of the strong DPA 1010 cm(-1) band (normalised to the ca. 2120 cm(-1) CNS- band) against DPA concentration gave a linear calibration (R2 = 0.986) over the range 0-50 ppm DPA. The inclusion of thiocyanate also allows false negatives due to accidental deactivation of the enhancing medium to be detected.

Surface-enhanced Raman spectroscopy as a probe of competitive binding by anions to citrate-reduced silver colloids.

Citrate-reduced silver colloids (CRSCs) are used extensively for surface-enhanced Raman scattering (SERS) studies of cations but are typically found to be ineffective for detection of anions unless they are treated with compounds that give them positively charged coatings. In this work CRSCs which were suitable for detection of anions were generated by treatment with aggregating agents that did not bind strongly to the silver surface. Under these conditions the major factor determining the enhancement of added anions was their ability to displace whatever anions were already present. In the case of CRSCs, residual citrate was observed when the colloids were aggregated with sulfate salts, since neither sulfate nor the residual nitrate displaced it. On addition of more strongly binding anions, such as halides, the citrate was displaced and the bands of the added analyte appeared, allowing them to be detected without the need for creation of positively charged coatings. It was found that the relative affinities of the anions, as determined by displacement experiments monitored by SERS, followed the solubilities of their silver salts, presumably because both properties are strongly dependent on the strength of the Ag-anion bonds. The relative affinities determine which anions can be detected in the presence of which others; nitrate, sulfate, and perchlorate are lower in the series than citrate and so are not observed. Displacement experiments show that dipicolinic acid (DPA) and Cl(-) have similar (stronger) binding, but they can be displaced in turn by Br(-) and I(-), which have the highest affinity and lowest solubility. This model allows a broad range of previous observations to be rationalized and allows the experimental conditions suitable for detection of particular new analytes to be designed on rational principles.

Rapid, quantitative analysis of ppm/ppb nicotine using surface-enhanced Raman scattering from polymer-encapsulated Ag nanoparticles (gel-colls).

Rapid, quantitative SERS analysis of nicotine at ppm/ppb levels has been carried out using stable and inexpensive polymer-encapsulated Ag nanoparticles (gel-colls). The strongest nicotine band (1030 cm(-1)) was measured against d(5)-pyridine internal standard (974 cm(-1)) which was introduced during preparation of the stock gel-colls. Calibration plots of I(nic)/I(pyr) against the concentration of nicotine were non-linear but plotting I(nic)/I(pyr) against [nicotine](x)(x = 0.6-0.75, depending on the exact experimental conditions) gave linear calibrations over the range (0.1-10 ppm) with R(2) typically ca. 0.998. The RMS prediction error was found to be 0.10 ppm when the gel-colls were used for quantitative determination of unknown nicotine samples in 1-5 ppm level. The main advantages of the method are that the gel-colls constitute a highly stable and reproducible SERS medium that allows high throughput (50 sample h(-1)) measurements.