Synthetic opioids, such as fentanyl and its analogues, are a new public health warning. Clandestine laboratories produce drug analogues at a faster rate than these compounds can be controlled or scheduled by drug agencies. Detection requires specific testing and clinicians may be confronted with a sequence of severe issues concerning the diagnosis and management of these contemporary opioid overdoses. This paper deals with methods for biological sample treatment, as well as the methodologies of analysis that have been reported, in the last decade, in the field of fentanyl-like compounds. From this analysis, it emerges that the gold standard for the identification and quantification of 4-anilinopiperidines is LC-MS/MS, coupled with liquid–liquid or solid-phase extraction. In the end, the return to the scene of illicit fentanyls can be considered as a critical problem that can be tackled only with a global multidisciplinary approach.

A surface-enhanced Raman scattering (SERS) platform for the selective trace analysis of Hg²⁺ ions was reported, based on poly-thymine (T) aptamer/2-naphthalenethiol (2-NT)-modified gold nanoparticles (AuNPs), which was an oligonucleotide-functionalized nanosensor and SERS chip. 2-NT was used as a Raman reporter, and T aptamer could form a T-Hg²⁺-T structure with Hg²⁺ ions making an SERS nanosensor absorbed to the SERS chip. The optimum concentrations of DNA and 2-NT were obtained. An average of 960 DNA molecules attached to each AuNP were measured. The limit of detection (LOD) was 1.0 ppt (1.0 × 10⁻¹² g/mL), which is far below the limit of 10.0 ppb for drinking water, stipulated by the World Health Organization. The sensor has the advantages of low detection cost, a simple sample pretreatment, a green solution and reducing false positives. Furthermore, the nanosensor was used for the determination of trace Hg²⁺ in the water of a lake; a reliable result was obtained accurately.

A novel gas-liquid separator (GLS) system for chelate vapor generation (Che-VG) combined with AFS was developed for the determination of trace Pb. It was shown that Pb can form a volatile chelate by mixing of Pb with ammonium O,O-diethyldithiophosphate (DEDTP) in various aqueous solutions. Under the optimal conditions (frit pores of the GLS, 5 – 15 μm; solution pH, 6.7; DEDTP concentration, 0.4%; flow rate of the two feed solutions in the on-line mode, 1.2 mL min⁻¹; and carrier gas flow rate, 150 mL min⁻¹), the calibration curve was linear up to 100 ng mL⁻¹ Pb. The limit of detection (LOD) was 1.1 ng mL⁻¹. The relative standard deviation was 5.6% for eleven replicate determinations of 10 ng mL⁻¹ Pb. The efficiency of Che-VG was estimated to be 12%, and the volatile Pb species was preliminarily studied by ICP-OES. This method was applied to determine trace Pb in water samples.

We apply interdigitated microelectrode array (IDA) sensors for water quality monitoring. IDA sensors with an ion-sensitive coating show higher sensitivity of about 600 mV with the hypochlorite ion concentration increasing from 0 to 10 ppm more than the traditional sensing method. The response mechanism and selectivity have been studied. Several material components that affect the sensing process were explored. Coupling agents and plasticizer were introduced into the coating material to improve the coating material quality and its adhesion to the electrodes. The stability/repeatability and linearity have been significantly improved.

Raman spectroscopy has been increasingly used in industrial production processes for analytical purposes. However, the quantitative analysis of complex mixtures based on their Raman spectra remains a problem, especially when not all of the spectra of pure components in the mixture are available. In this work, a method for the quantitative analysis of a key component in complex mixtures based on peak decomposition is introduced. The proposed method only requires the spectrum of the main component in the mixture before analysis. The spectra of the mixture are decomposed to the contributions of the main component and a group of parametric Lorentzian functions. Then, the representative peaks of the key component are extracted. Finally, a calibration model is established. This method is applied to a complex mixture containing m-xylene, o-xylene, p-xylene, ethylbenzene, methylbenzene, three trimethylbenzenes, non-aromatic hydrocarbons, etc. to determine the concentration of o-xylene in the mixture. Experiments demonstrate that the proposed method performs better than the commonly-used partial least squares (PLS), especially when the number of training samples is very small.

An analytical method for the determination of sialic acids in biological samples has been developed and applied to fetal bovine serum (FBS), newborn calf serum and adult bovine serum. The hydrolysis of sera was carried out and the liberated sialic acids were quantified using a rapid and sensitive HPLC. The HPLC includes the separation and detection of N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) using hydrophilic interaction liquid chromatography and a fluorometric post-column reaction with 2-cyanoacetamide. The calibration graphs for Neu5Ac and Neu5Gc were linear over the range of 10 pmol – 5 nmol. The concentrations of sialic acids in FBS, newborn calf serum and adult bovine serum were 5.06, 3.79 and 1.64 mM, respectively. The ratios of Neu5Gc and Neu5Ac changed dramatically according to the development stages. The present method has a satisfactory sensitivity in the quantification of Neu5Ac and Neu5Gc in serum samples. It seems that this analytical system can therefore be applied for routine use in clinical investigations of serum sialylation changes in cancer patients.

Barium (Ba) isotopes have been booming while providing ubiquitous traceability to various geochemical/oceanographical processes in recent years. Accurate and precise determinations of Ba isotopes is the main precondition to apply them to tracing various processes. However, a particular determination method is lacking for Ba isotopic ratios in river water. Compared to the double-spike method which needs expensive spikes, intensive laboratory operation, and complex calibration, sample-standard bracketing (SSB) is an easier and more convenient method to obtain isotopic data on the multiple collector inductively coupled plasma mass spectrometer. In this study, to obtain the Ba isotopic ratio of river-water samples with a rather lower Ba concentration than igneous rock, we experimented with K, Ca, Na, Mg, and Ce doping tests. The acidity and concentration matches to explore suitable SSB method conditions for river water Ba isotopic determinations on an MC-ICP-MS. The results showed no obvious matrix effects to Ba isotopes when K/Ba, Ca/Ba, Na/Ba, and Mg/Ba <5, and Ce/Ba <0.2, indicating that the matrix effects are negligible after column purification of Ba. HNO₃ concentration match tests showed that within a 25% acidity difference, there would be also no systematic effects to a Ba isotopic determination. However, Ba isotopic determinations are highly sensitive to the Ba concentration difference between the standard and the sample. We observed a mismatch between the Ba concentration and its isotopic ratios, even when the concentration was strictly within a 5% difference. Nevertheless, the on-peak zero strategy (i.e. subtraction of HNO₃, gas, and instrumental blanks) worked well to solve the mismatch situation. With this easy strategy, the Ba isotopic ratios of batch natural rive-water samples with various Ba concentrations will become easily accessible.

An electrochemical analysis of polyphenols (theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3′-gallate (TF2B), theaflavin-3,3′-digallate (TF3), and epigallocatechingallate (EGCG)) in a black tea infusion is demonstrated. The characterization of each polyphenol in a solution containing only a single type of polyphenol for a redox reaction at the CNT electrode with cyclic voltammetry (CV) was conducted. The oxidation peak at around +0.30 V for TF1 is assigned to catechol group in a benzotropolone ring. The oxidation peak at around +0.35 V for TF2A, TF2B, and TF3 is assigned to both of the catechol groups in the benzotropolone ring and the pyrogallol group in the gallate ring. The oxidation peak at around +0.35 V for EGCG is assigned to a pyrogallol group in the gallate ring. Current changes of those individual polyphenols at the peak potential are proportional to their concentrations (linear range 0.28 – 94 μM; detection limit 0.11 μM). The CV curve for real black tea, which is mainly composed of a mixture of the mentioned five compounds, is produced by the sum of those. The current change of the mixture solution of polyphenols is also proportional to the mass concentration of the total polyphenols and the sensitivity defined as the slope of current vs. concentration plot is independent of the ratio of the individual polyphenols. This indicates that the peak current at around +0.35 V can quantify the total amount of polyphenols in a black tea. Additionally, the shape of the CV curve can roughly estimate the ratio of [catechins]/[theaflavins]. The values for real samples determined from CVs show good agreement with that obtained by high-performance liquid chromatography.

An effective flow injection analysis (FIA) system employing paired emitter detector diode (PEDD) for simultaneous dual antioxidant assays is proposed. The total antioxidant capacity (TAC) was measured using the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay in parallel with the ferric reducing antioxidant power (FRAP) assay. Ascorbic acid was used as the reference antioxidant and the TAC value reported as ascorbic acid equivalent (AAE). A 10-port valve furnished with two injection loops allowed the sample from one loop to react with the ABTS reagent and be detected by one PEDD. At the same time, the sample from the second loop reacted with the FRAP reagent and is detected at the second PEDD. A pair of red light emitting diodes (634 nm) was employed for both PEDDs. The linearity range was 10 to 50 μM ascorbic acid, with limit of detection of 3.18 and 4.37 μM, and precision of 2.41 and 2.15% RSD (for 30 μM ascorbic acid, n = 10) for the ABTS and FRAP assay, respectively. Sample throughput of 90 samples/h was achieved. The method was applied to the measurement of TAC of commercial fruit juice, instant tea products and vitamin C tablets. The observed AAE values were in good agreement with those obtained using batch methods with a spectrophotometer.

The less stability and robustness, high-cost preparation and maintenance of natural enzymes, especially horseradish peroxidase (HRP), challenge researchers to introduce effective alternatives for their wide applications. Herein, the peroxidase-like activity of AuCu bimetal nanoclusters (AuCu NCs) was investigated in the rhodamine B–H₂O₂ chemiluminescence (CL) system. AuCu NCs could effectively catalyzed the CL reaction, and a high intensive emission intensity was obtained. A comprehensive study was implemented to examine the effects of different stabilizing ligands and Au/Cu ratios on the catalytic activity of obtained NCs. Comparison experiments were also expanded to include Au and Cu nanoparticles with different sizes, too. The results verified the superior catalytic activity of penicillamine-stabilized AuCu bimetal NCs containing 50% cu atoms. Finally, the analytical application of the introduced CL system showed great sensitivity for H₂O₂ detection, with a detection limit of 0.13 nM. Moreover, the developed CL method was able to measure glucose and xanthine over wide concentration ranges of 0.1 – 400 and 0.1 – 200 μM, respectively. The method also indicated satisfactory reliability, confirmed by standard reference materials.

A simple and sensitive chemiluminescent (CL) sensing platform for mercury(II) ions (Hg²⁺) in water was developed based on monolayer molybdenum disulfide (MoS₂). The layered MoS₂ can catalyze the oxidation of luminol by H₂O₂, producing an enhanced CL signal because of the peroxidase-like activity of the layered MoS₂. In addition, MoS₂ has a good adsorption ability to Hg²⁺ because of the inherent affinity of Hg²⁺ to sulfur contained in MoS₂. Interestingly, the pre-incubation of Hg²⁺ with layered MoS₂ inhibited the catalytic activity of MoS₂ on the luminol–H₂O₂–MoS₂ CL reaction, leading to CL quenching. The CL intensity decreased linearly with increasing concentration of Hg²⁺ from 0.005 – 40 μM. The limit of detection (LOD) was estimated to be 1 nM. The relative standard deviation (RSD) was found to be 3.71%, indicating good reproducibility. The recoveries of Hg²⁺ spiked in tap water were from 100.0 to 116.0% with RSD from 2.7 to 5.6%, detected by the standard addition method, and demonstrated good applicability.

Trace elements contained in single-crystal gallium nitride (GaN), which is a refractory material, were determined by inductively coupled plasma mass spectrometry with laser ablation in liquid (LAL) sampling. Particle size analysis by dynamic light scattering confirmed that LAL atomized the single-crystal GaN, and scanning electron microscopy/energy-dispersive X-ray spectrometry revealed that LAL sampling converted the GaN to gallium oxide particles. The atomization and changes in the chemical composition allowed for easy digestion of the sampled particles with nitric acid and a hot plate instead of with hydrochloric or sulfuric acid, a microwave digestion system, and a high-pressure vessel. Trace element analysis revealed the presence of trace Mg, Ge, Y, and Cd in single-crystal GaN, and the detection limits for these elements were 0.1 – 2 mg kg⁻¹. The uncertainty derived from the small amount of sample used, which is a disadvantage of LAL sampling, was reduced by calculating the amount of sample ablated by measuring the concentration of the major element, Ga. We expect that the trace-element profiles of other refractory materials will be able to be determined by using this analytical approach.

Even though large number of individually addressable electrodes can be effectively assembled in a small area, electrochemical detection methods have a relatively limited ability to detect multiple analytes compared to microdialysis probes and other analytic techniques. Here, we report a facile method for the electro-addressable functionalization of a probe comprising of closely spaced three individually addressable carbon fiber electrodes (CFEs) for the detection of nucleic acids. First, a multi electrode array probe comprising three adjacent CFEs was fabricated through pulling a three-barrel glass capillary with a single carbon fiber in each barrel. Second, electropolymerization based doping was used for the electro-addressable functionalization of the multi-electrode array probe. To demonstrate that the current strategy works, anti-miR-34a was electrografted on only one of three electrodes by the electropolymerization of pyrrole on a specific electrode. A second electrode was coated only with polypyrrole (PPy) and the third was left unmodified. The results demonstrate that the present strategy has great potential for constructing multiplex nucleic acid micro/nano biosensors for local and in situ detection of multiple nucleic acid molecules, such as miRNAs at a time.

Although Raman shifts originate from molecular vibrations and in theory must be independent of analytical systems, acquired Raman shifts, in practice, are not so. Since the consistency of Raman shifts acquired with different systems has not been investigated previously, we have compared the Raman spectra of polystyrene, benzonitrile, and cyclohexane obtained with 26 different systems. The medians of 26 measurements for the characteristic peaks were found to be 1001.3, 1001.1, and 802.0 cm⁻¹ for polystyrene, benzonitrile, and cyclohexane, respectively, and were consistent with their corresponding ASTM E1840 values, which have been widely used for the calibration of Raman systems. However, only 16 measurements of the Raman shift of the polystyrene peak (1001.4 cm⁻¹) met the tolerance standard of the European Pharmacopoeia (±1.5 cm⁻¹). Thus, consistency of Raman shifts obtained using different systems is low, and this mainly originates from differences in the Raman systems rather than materials. Although correction of the offset using the Raman shift of the peaks of cyclohexane (802.0 or 2852.4 cm⁻¹) could improve the consistency of the Raman shifts acquired with different systems, the magnitude of improvement was not uniform over the range of shift values. Thus, there is a need for a standardized calibration protocol that can be used for multiple Raman shifts of common materials to improve the consistency of Raman shifts for different systems.

Single cell analysis has gained attention as a means to investigate the heterogeneity of cells and amplify a cell with desired characteristics. However, obtaining a single cell from a large number of cells remains difficult because preparation of single-cell samples relies on conventional techniques such as pipetting that are labor intensive. In this study, we developed a system combining a 0.6-mm thin glass microfluidic device and machine vision approach to isolate single Euglena gracilis cells, as a model of microorganism with mobility, in a small/thin glass chamber. A single E. gracilis cell in a chamber was cultured for 4 days to monitor its multiplication. With this system, we successfully simplified preparation of single cells of interest and determined that it is possible to combine it with other analytical techniques to observe single cells continuously.

Nucleobase-modified aptamers are attractive candidates for diagnostic and therapeutic agents due to the high affinity, stability and functionality. However, since even conventional SELEX requires many selection rounds, acquisition of modified aptamers is much more laborious. Herein, microbeads-assisted capillary electrophoresis (MACE)-SELEX was applied against thrombin using the indole-modified DNA library. After only three selection rounds, we successfully enriched the modified aptamers and they showed slower off-rate than reported aptamers, suggesting MACE-SELEX is a promising approach for rapid identification of modified aptamers.

We demonstrated a simple and rapid deacetylation reaction of p-nitrophenyl thioacetate by cyanide ion. This reaction is caused by the strong nucleophilic tendency of the cyanide ion to the electrophilic substrate and has been previously reported as the most common method for detecting cyanide ions. Tetrabutylammonium cyanide and sodium cyanide can be used as sources of cyanide ions for catalytic deacetylation reactions. Both catalysts showed almost the same catalytic reaction and the catalytic reaction was instantaneous at room temperature with a minimum concentration of cyanide ions of up to 1.0 μM. Cyanide did not catalyze the deacetylation reaction of p-nitropnenyl acetate due to a decrease in the nucleofugality of the leaving group and a decrease in the electrophilicity of carbonyl carbon in the substrate. However, the only disadvantage of this reaction system is the interference with other anions, such as acetate and azide, which also have nucleophilicity toward an electrophilic substrate. If these problems are improved, the system could be applied as a very efficient cyanide ion sensor.

An automatic management system for nutrient solutions was constructed using a programmable logic controller (PLC) and a K⁺-ion selective electrode (K⁺-ISE). The concentration of K⁺ was monitored by the K⁺-ISE. When the concentration of K⁺ fell to the threshold limit, an appropriate amount of a concentrated K⁺ solution was added to the hydroponic solution. The volume was also maintained at a constant level by addition of water. This system can be constructed simply and inexpensively without any computers and pumps.