Current Analytical Chemistry - Volume 17, Issue 3, 2021

Background: Ultrasmall nanoclusters (USNCs) have attracted tremendous attention owing to their unique properties that make them desirable for the development of personalized medicine, such as tunable emission, straightforward modification, and renal clearance. Hence, USNCs have emerged as potential materials for nanotheranostics. Objective: For decades, great efforts have been devoted to the bio-applications of USNCs, promising platforms to satisfy the increasing demand for precise diagnostic and targeted therapeutics. Herein, we summarize the most recent advances of USNCs in biomedical applications and provide our perspective on the future development of USNCs. Results: This review briefly summarized the synthetic methods of metallic USNCs and discussed their recent applications for cancer imaging and therapy. Conclusion: USNCs have shown their potential for accurate diagnosis and specific delivery of therapeutics in preclinical research.

Background: Luminogens that feature aggregation induced emission (AIE) are typically non-emissive in solution but become highly luminescent upon aggregation in poor solvents or solid state. Discussion: Unlike conventional fluorophores that exhibit aggregation-caused quenching (ACQ), utilization of AIE luminogens as bioprobes has featured superior photostability, low background signal, large Stokes’ shifts, high sensitivity and turn-on luminescent response. Conclusion: The versatility of AIE-based luminogens as bioprobes has been demonstrated through various applications in cell organelle imaging, ion sensing and sensitive detection of biomacromolecules. Examples of AIE-based luminogens and their applications as luminescent sensors for biosensing and optical imaging are discussed herein.

Background: Cold stress injury to plants is a highly complex process and a significant cost to agricultural food production. This stress adversely affects metabolism, growth and productivity of plants. Timely visualization of plants’ cold stress is important for identifying injury to the plants and for predicting a plant's survival. While there is a developed understanding of physiology and biology associated with this condition, early detection and assessment of the injury remain difficult. A rapid, remote method for quantitatively measuring cold stress in situ will aid producers in selecting cold-tolerant plants for breeding and for identifying appropriate remedies. Methods: Standard methods such as electrolyte leakage assays correctly and quantitatively evaluate the damage. However, these methods are laborious and costly, not applicable for non-invasive highthroughput screening of plants in the field. To address this problem, we have evaluated a new sensitive method based on the fluorescence lifetime imaging (FLIM) that can be used for injury assessment. Results: Standard methods such as electrolyte leakage assays correctly and quantitatively evaluate the damage. However, these methods are laborious and costly, not applicable for non-invasive highthroughput screening of plants in the field. To address this problem, we have evaluated a new sensitive method based on the fluorescence lifetime imaging (FLIM) that can be used for injury assessment. We have demonstrated that the fluorescence lifetime of chlorophyll’s autofluorescence in intact leaves from Periwinkle (Vinca Minor) plants is correlated with the degree of injury. Nonlinear regression identifies the long-lifetime component of the fluorescence decay, showing a high sensitivity for detecting injury mere minutes after plant exposure to -20°C, while no gross visual differences could be distinguished. Moreover, conventional color imaging, reflection, or and steady-state fluorescence intensity showed lower sensitivity in detecting cold stress. Conclusion: FLIM was shown to be more sensitive than visual or camera-based inspection and can be potentially used for rapid and remote monitoring of the health of individual plants and crops in the field and will aid in the selection of cold-tolerant crop variants.

Background: The ubiquitous Lewis acid/base interactions are important in solution processes. Analytical chemistry may benefit from a better understanding of the role of Lewis basicity at the molecular level or acting through a bulk solvent effect. Objective: To delineate (i) the basicity at a molecular level, hereafter referred to as solute basicity, and (ii) the solvent basicity, which is a bulk-liquid property. Methods: The literature that relates Lewis basicity scales and solvent effects is analyzed. A special focus is placed on two extensive scales, the Donor Number, DN, and the BF3 Affinity scale, BF3A, which were obtained by calorimetric measurements on molecules as solutes diluted in a quasi-inert solvent, and therefore define a molecular Lewis basicity. We discuss the validity of these solute scales when regarded as solvent scales, in particular when the basicity of strongly associated liquids is concerned. Results: We demonstrate the drawbacks of confusing the Lewis basicity of a solvent molecule, isolated as a solute, and that of the bulk liquid solvent itself. Conclusion: Consequently, we recommend a reasoned use of the concept of Lewis basicity taking clearly into account the specificity of the process for which a Lewis basicity effect may be invoked. In particular, the action of the Lewis base, either as an isolated entity or as a bulk liquid, must be distinguished.

Background: Over the last few decades, there has been a growing interest in Two- Dimensional Liquid Chromatography (2D-LC). This advanced technology has become a relevant solution for solving all the analytical challenges encountered in the pharmaceutical industry. The primary purpose of this review is to give a brief account of the developing techniques notable in 2D-LC. Methods: Review of recent literature on advanced separation techniques for complex mixtures revealed that 2D-LC is the most widely used technique in the pharmaceutical laboratory for the separation of complex samples. Among the various techniques used in 2D-LC, comprehensive 2D-LC and heart-cutting 2D-LC are highly used techniques. To enhance the resolution, further development has been made to heart-cutting 2D-LC called multiple heart-cutting 2D-LC, which has recently become a very popular technique in the pharmaceutical industry. Therefore research articles mentioning the use of multiple heart-cutting 2D-LC for separation of complex mixtures were reviewed. Results: The most crucial benefit of multiple heart-cutting 2D-LC is its reduced effort in method development and also the storage of multiple sample sections for further analysis. The multiple heartcutting 2D-LC is suited, preferably for method development and impurity analysis of pharmaceutical substances, fine chemicals and offers better peak separation, which is otherwise not possible by comprehensive 2D-LC. Conclusion: The advantage of two-dimensional liquid chromatography over one-dimensional liquid chromatography is its high resolving power. Further improvement in resolution was achieved by using the advanced multiple heart-cutting 2D-LC which appears to have an imperative role in pharmaceutical and food analysis.

Background: Chiral purity is a critical quality attribute of pharmaceutical materials as chiral compounds are known to exhibit different pharmacological and toxicological properties as compared to those of their enantiomers (or diastereomers for molecules with multiple chiral centers). It is important to note that about 40% of the synthetic drugs are chiral, 60% of all pharmaceuticals are chiral and 45% chiral drugs are sold as racemates. The objective of the current review is to discuss various chromatographic techniques used for the separation of chiral compounds. Methods: Various bibliographic databases of previously published peer-reviewed research papers were explored and systematic data has been compiled in terms of various chromatographic techniques used for chiral compounds’ separation. A comparison of different techniques as well as their advantages is also discussed. Results: A comprehensive review of 130 papers including both, research and review articles, was carried out. The analytical techniques have been discussed in detail. Apart from chromatographic techniques, other techniques such as circular dichroism, nuclear magnetic resonance, UV-visible spectroscopy using cyclodextrin derivatives have also been highlighted. Conclusion: The pharmaceutical industries need analytical methods to conclude enantiomeric concentration and obtain a drug with a single stereo configuration. Sensitive techniques such as HPLC, GCMS and LCMS, etc. are used for identification and quantification of single enantiomers, specifically in drug discovery and development.

Background: Neurotransmitters are chemical messengers with crucial implication in the human body. Perturbations in the concentration of neurotransmitters can affect a multitude of mental and physical functions such as heart rate, sleep, appetite and mood. Thus, the sensitive detection of these compounds is a real need for a new generation of treatments. Methods: Simultaneous detection of two important neurotransmitters, namely dopamine and serotonin, was investigated in this study using differential pulse voltammetry. The optimization of several surface parameters was performed in order to choose the best electrode material for electrochemical oxidation of targets. Screen-printed electrodes based on carbon, gold and platinum and modified with different nanomaterials (carbon nanotubes, gold nanoparticles and carbon nanotubes decorated with gold nanoparticles) were tested. Results: Carbon-based electrodes modified with multiwall carbon nanotubes and gold nanoparticles were chosen after the optimization protocol. Linear correlations between the analytic signals obtained and the concentration of dopamine and serotonin, respectively were obtained with good sensitivity and the detection limits were 0.3 μM for dopamine and 0.8 μM for serotonin with no significant reciprocal influences. Selectivity studies were also performed, as well as tests in real samples (e.g., human serum, tears and saliva) complex matrices for which acceptable recoveries were obtained. Conclusion: The results obtained in this study can be considered as an important starting point for the development of a fast and simple method for selective and highly sensitive detection of neurotransmitters, with possible applications in the diagnosis of different pathologies and for monitoring the effectiveness of the applied drug treatment.

Background: 5-fluorouracil and resveratrol are the two most effective anticancer drugs. Combination therapy with these two drugs has shown promising results in cancer. The formulation containing 5-fluorouracil and resveratrol has been prepared, but no analytical method is available in the literature for their simultaneous estimation. However, several analytical methods are there for estimation of either 5-fluorouracil or resveratrol alone. Therefore, the present article is designed for the simultaneous estimation of 5-fluorouracil and resveratrol by HPLC and its application in the quantification of the drugs present in the formulated nanostructured lipid carrier (NLC). Methods: The method was developed using a C18 column (Purospher® STAR RP-18 endcapped (5 μm) Hibar® RT 250-4.6) with acetonitrile and water as the mobile phase (25:75 v/v) and estimated at 272 nm. The currently developed method was further validated by the ICH guideline Q2 (R1). Combinatorial NLC of 5-fluorouracil and resveratrol was also prepared and characterized. Results: The LOD and LOQ were 8.22 and 24.91 μg mL^-1 and 6.58 and 19.93 μg mL^-1, respectively. The precision was under the acceptable limits of <2% RSD. The content of 5-fluorouracil and resveratrol in NLC were found to be 99.452% and 96.421%, respectively. Conclusion: The findings showed that the developed and validated method was simple, fast, costeffective, and reproducible for the simultaneous estimation of both the drugs in the same formulation.

Background: Measuring medicinal compounds to evaluate their quality and efficacy has been recognized as a useful approach in treatment. Rhubarb anthraquinones compounds (mainly including aloe-emodin, rhein, emodin, chrysophanol, and physcion) are the main effective components in purgating drug. In the current Chinese Pharmacopoeia, the total anthraquinones content is designated as its quantitative quality and control index, while the content of each compound has not been specified. Methods: On the basis of forty rhubarb samples, the correlation models between the near infrared spectra and UPLC analysis data were constructed using support vector machine (SVM) and partial least square (PLS) methods, according to the Kennard and Stone algorithm for dividing the calibration/ prediction datasets. Good models mean they have high correlation coefficients (R²) and low root mean squared error of prediction (RMSEP) values. Results: The models constructed by SVM have much better performance than those by PLS methods. The SVM models have high R2 of 0.8951, 0.9738, 0.9849, 0.9779, 0.9411, and 0.9862 that correspond to aloe-emodin, rhein, emodin, chrysophanol, physcion and total anthraquinones contents, respectively. The corresponding RMSEPs are 0.3592, 0.4182, 0.4508, 0.7121, 0.8365, and 1.7910, respectively. 75% of the predicted results have relative differences being lower than 10%. As for rhein and total anthraquinones, all of the predicted results have relative differences being lower than 10%. Conclusion: The non-linear models constructed by SVM showed good performances with predicted values close to the experimental values. This can perform the rapid determination of the main medicinal ingredients in rhubarb medicinal materials.

Background: Although molecularly imprinted polymers (MIPs) have now been widely utilized for the sample pre-treatment, chromatography separation and removal of pollutants, conventional MIPs still lack satisfactory compatibility with water, thus leading to poor molecular recognition for target analytes in aqueous solutions. The aim of the study was to prepare water-compatible MIPs. Methods: The zwitterionic MMIPs were synthesized on vinyltrimethoxysilane-coated Fe3O4 (Fe3O4-VTMS) through a surface imprinting process by using levofloxacin (LEV) as a template, [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SPE) as a functional monomer, N, N-methylene-bis-acrylamide (MBA) as a crosslinker and potassium persulfate as an initiator. Results: The prepared zwitterionic LEV-MMIPs were characterized by Fourier transform infrared spectrometry, X-ray diffraction, vibrating sample magnetometry, scanning electron microscopy and water contact angle test. The characterization results showed that zwitterionic LEV-MMIPs exhibited good magnetic responsiveness and super-hydrophilicity (the contact angle is 0°). The optimum pH for binding LEV was found to be 6.0 and the binding isotherm followed the Langmuir isotherm model of monolayer adsorption. The binding process was very fast and the pseudo-second-order model fitted well with the kinetic data. The adsorption capacity of these zwitterionic MMIPs was 54.30 mg g^-1 with a selectivity factor of 1.6 compared to the magnetic non-imprinted polymers (MNIPs). Their feasibility for removing fluoroquinolones (FQs) from the environmental sample was demonstrated using pearl river water spiked with LEV, gatifloxacin, ciprofloxacin and lomefloxacin. The zwitterionic LEV-MMIPs could be reused at least five times with a removal efficiency of more than 80% for the selected FQs. Conclusion: The prepared zwitterionic LEV-MMIP is a promising sorbent for rapid, selective and efficient removal of fluoroquinolones from aqueous medium.

Background: An electrochemical DNA biosensor based on gold nanoparticles (AuNPs) and thiol graphene (TGR) nanocomposite modified carbon ionic liquid electrode (CILE) was developed to detect a specific nuc gene of Staphylococcus aureus, which was further used in the analysis of PCR amplification samples from unfrozen pork. Objective: The development of a DNA biosensor derived from AuNPs-coated TGR could be used as a novel sensing method for the detection of specific ssDNA sequences in biological and clinical samples. Methods: The electrochemical properties of modified CILE electrodes were determined by cyclic voltammetry and electrochemical impedance spectroscopy, and the electrochemical performances of the biosensor were investigated by differential pulse voltammetry. Results: This gene sensor was able to detect the specific nuc gene from Staphylococcus aureus over the concentration range from 1.00^-15 mol L^-1 to 1.00^-6 mol L^-1 with a limit of detection of 4.50^-16 mol L^-1 (3σ), and it was applied in the detection of Staphylococcus aureus in an unfrozen pork sample after PCR amplification of the nuc gene with satisfactory results. Conclusion: This gene biosensor showed high sensitivity and good selectivity, wide detection range and low detection limit, which demonstrated an effective tool to detect specific nuc gene sequences of Staphylococcus aureus.

Background: Tramadol, (±)-trans-2-[(dimethylamino) methyl]-1-(3-methoxyphenyl) cyclohexanol, is a synthetic centrally acting analgesic used in the treatment of moderate to chronic pain. Tramadol, like other narcotic drugs, is used for the treatment of pain and may also be abused. Its overdose can cause adverse effects such as dizziness, vomiting, and nausea. The aim of this paper is to develop a sample preparation method for the determination of tramadol in human plasma samples, followed by CE analysis. Methods: Ultrasound assisted-dispersive liquid-liquid microextraction using binary mixed extractant solvent (chloroform and ethyl acetate) was used for the extraction of one hundred microliters of tramadol spiked human plasma samples and in real human plasma samples obtained from the patients with abuse of tramadol. After evaporation of the extractant solvent, the residue was reconstituted in 100 μL deionized water and subsequently analyzed by CE-UV. Results: The developed method has remarkable characteristics, including simplicity, good repeatability and appreciable accuracy. Under the best extraction conditions, a low limit of detection at 7.0 μg per liter level with good linearity in the range of 0.02-10 μg mL^-1 was obtained. Conclusion: UA-DLLME, using a binary mixed extraction solvent, was established for the determination of tramadol in human plasma samples via the CE method with UV-detection. In addition, the analysis of tramadol in some plasma samples of patients with abuse of tramadol indicated that the method has acceptable performance for the determination of tramadol in plasma samples, which indicates that the method is suitable for clinical applications.