There has been an increasing demand for rapid and sensitive techniques for the identification and quantification of pharmaceutical compounds in human biofluids during the past few decades, and surface-enhanced Raman scattering (SERS) is one of a number of physicochemical techniques with the potential to meet these demands. In this study we have developed a SERS-based analytical approach for the assessment of human biofluids in combination with chemometrics. This novel approach has enabled the detection and quantification of the β-blocker propranolol spiked into human serum, plasma, and urine at physiologically relevant concentrations. A range of multivariate statistical analysis techniques, including principal component analysis (PCA), principal component–discriminant function analysis (PC-DFA) and partial least-squares regression (PLSR) were employed to investigate the relationship between the full SERS spectral data and the level of propranolol. The SERS spectra when combined with PCA and PC-DFA demonstrated clear differentiation of neat biofluids and biofluids spiked with varying concentrations of propranolol ranging from 0 to 120 μM, and clear trends in ordination scores space could be correlated with the level of propranolol. Since PCA and PC-DFA are categorical classifiers, PLSR modeling was subsequently used to provide accurate propranolol quantification within all biofluids with high prediction accuracy (expressed as root-mean-square error of predictions) of 0.58, 9.68, and 1.69 for serum, plasma, and urine respectively, and these models also had excellent linearity for the training and test sets between 0 and 120 μM. The limit of detection as calculated from the area under the naphthalene ring vibration from propranolol was 133.1 ng/mL (0.45 μM), 156.8 ng/mL (0.53 μM), and 168.6 ng/mL (0.57 μM) for serum, plasma, and urine, respectively. This result shows a consistent signal irrespective of biofluid, and all are well within the expected physiological level of this drug during therapy. The results of this study demonstrate the potential of SERS application as a diagnostic screening method, following further validation and optimization to improve detection of pharmaceutical compounds and quantification in human biofluids, which may open up new exciting opportunities for future use in various biomedical and forensic applications.

In this study surface enhanced Raman scattering (SERS) combined with the isotopic labelling (IL) principle has been used for the quantification of codeine spiked into both water and human plasma. Multivariate statistical approaches were employed for the analysis of these SERS spectral data, particularly partial least squares regression (PLSR) which was used to generate models using the full SERS spectral data for quantification of codeine with, and without, an internal isotopic labelled standard. The PLSR models provided accurate codeine quantification in water and human plasma with high prediction accuracy (Q²). In addition, the employment of codeine-d₆ as the internal standard further improved the accuracy of the model, by increasing the Q² from 0.89 to 0.94 and decreasing the low root-mean-square error of predictions (RMSEP) from 11.36 to 8.44. Using the peak area at 1281 cm⁻¹ assigned to C–N stretching, C–H wagging and ring breathing, the limit of detection was calculated in both water and human plasma to be 0.7 μM (209.55 ng mL⁻¹) and 1.39 μM (416.12 ng mL⁻¹), respectively. Due to a lack of definitive codeine vibrational assignments, density functional theory (DFT) calculations have also been used to assign the spectral bands with their corresponding vibrational modes, which were in excellent agreement with our experimental Raman and SERS findings. Thus, we have successfully demonstrated the application of SERS with isotope labelling for the absolute quantification of codeine in human plasma for the first time with a high degree of accuracy and reproducibility. The use of the IL principle which employs an isotopolog (that is to say, a molecule which is only different by the substitution of atoms by isotopes) improves quantification and reproducibility because the competition of the codeine and codeine-d₆ for the metal surface used for SERS is equal and this will offset any difference in the number of particles under analysis or any fluctuations in laser fluence. It is our belief that this may open up new exciting opportunities for testing SERS in real-world samples and applications which would be an area of potential future studies.

Raman spectroscopy has attracted considerable interest during the past two decades as a vibrational technique used for the molecular characterisation of different molecules. Whilst the Raman effect is known to be generally weak, it is also known that this can be greatly improved using surface-enhanced Raman scattering (SERS). Indeed, in recent years, the power of SERS for rapid identification and quantification of target analytes in a wide range of applications has been repeatedly demonstrated in multiple studies. Moreover, the application of SERS in combination with an isotopically labelled compound (ILC), as an internal standard, has also very recently shown promising results for quantitative SERS measurements, by improving both its accuracy and precision. This is due to the ¹²C and ¹³C or ¹H and ²H (D) having similar physicochemical properties. The use of these internal standards results in the reduction of any influences due to the number of nanoparticles within the analysis zone and fluctuations in laser fluence. Thus, in this study we have employed SERS for quantitative detection of tryptophan (Trp) and caffeine. These have been chosen because Trp is readily available as the deuterated form and caffeine is available in both ¹²C and ¹³C. Quantum chemical calculations based on density functional theory (DFT) have been utilized to determine the vibrational characteristics of the target analytes. For SERS analysis incorporating isotopologues of tryptophan three independent experiments were conducted with three different batches of nanoparticles over a 12 month period; our results show that the use of this internal standard improves quantification of this target molecule. In particular for the independent test sets (i.e., samples not used in quantitative partial least squares regression (PLSR) model construction) we observed improvements in the linearity for test set predictions, as well as lower errors in test set predictions, when isotope internal standards were used during SERS for both deuterated tryptophan as well as ¹³C caffeine. This work is an extension of and a natural progression from our earlier studies. By exploring additional analytes of interest, allowing for the assessment of the different types of stable isotopes as internal standards, and demonstrating the transfer/robustness of isotopologues for use with SERS, we believe this approach could be readily extended to other biologically-relevant compounds.

Textiles that respond to external stimuli with a change in their properties are referred to as “smart clothing”. Fluorescent textiles, which change color in response to light, are a subset of smart textiles. Herein, fluorescent and hydrophobic composite coatings were prepared and applied onto cellulose-based fabrics by the pad-dry-curing method. This innovative approach involves the integration of lanthanide-doped aluminum strontium oxide pigment phosphor nanoparticles into room temperature vulcanized silicone rubber. The pigment phosphor nanoparticles must be uniformly dispersed without agglomeration in order to create a transparent nanocomposite film. The pad-dry-cured film was successfully cured onto the cotton fabric under ambient conditions. The superhydrophobic activity of the fluorescent fibers improved with increasing pigment content. Both the ultraviolet protection and the antibacterial properties of the coated fibers were also investigated. The generated translucent fluorescent layer exhibited an absorbance peak of 358 nm and an emission peak of 517 nm. The fluorescent cotton fibers exhibited different colors, including white under visible daylight and intense green under ultraviolet devices, as described by the CIE Lab, as well as decay time, excitation and emission spectra. Both the mechanical performance and comfortability of the coated fibers were tested by measuring air permeability and bend length. The spectroscopic results of the treated fabrics are detailed using a scanning electron microscope and energy dispersive X-ray spectra. During ultraviolet stimulation, the coated cloth displayed a reversible and fast fluorescent photochromism that was not fatigued. The qualities of colorfastness were described, including washing, crocking, sweat, and light.