Aptamers, single-stranded DNAs/RNAs with a strong and specific interaction towards a target molecule, have wide applications in the fields of medicine and biosensors. In conventional aptamer selection methods, it is difficult to obtain “preorganized” and/or “induced-fit” type of aptamers selectively. In this study, separation and fractionation of single-stranded DNAs with/without stable preorganized structures were carried out using capillary sieving electrophoresis. The fractionated DNAs showed different mobilities and thermodynamic stabilities of their secondary structures; this outcome is deemed to be necessary for the synthesis of novel aptasensors with a desirable sensing mechanism.
We proposed selective manipulation techniques for retrieving and retaining target cells arrayed in microwells based on dielectrophoresis (DEP). The upper substrate with microband electrodes was mounted on the lower substrate with microwells based on the same design of microband electrodes by 90 degree relative to the lower substrate. A repulsive force of negative dielectrophoresis (n-DEP) was employed to retrieve the target cells from the microwell array selectively. Furthermore, the target cells were retained in the microwells after other cells were removed by n-DEP. Thus, the system described in this study could make it possible to retrieve and recover single target cells from a microwell array after determining the function of cells trapped in each microwell.
A hydrogel is a solid form of polymer network absorbed in a substantial amount of aqueous solution. In electrophoresis, hydrogels play versatile roles including as support media, sieving matrixes, affinity scaffolds, and compositions of molecularly imprinting polymers. Recently, the study of hydrogels has been advancing with unprecedented speed, and the application of hydrogels in separation science has brought new opportunities and possible breakthroughs. A good understanding about the roles and effects of the material is essential for hydrogel applications. This review summarizes the hydrogels that has been described in various modes of electrophoretic separations, including isoelectric focusing gel electrophoresis (IEFGE), isotachophoresis (ITP), gel electrophoresis and affinity gel electrophoresis (AGE). As microchip electrophoresis (ME) is one of the future trends in electrophoresis, thought provoking studies related to hydrogels in ME are also introduced. Novel hydrogels and methods that improve separation performance, facilitate the experimental operation process, allow for rapid analysis, and promote the integration to microfluidic devices are highlighted.
Nowadays, resorcinol (RC) has been widely applied in the chemical and pharmaceutical industries. However, the electrochemical detection technique of RC still features some significant drawbacks, for instance, a low sensitivity. Hence, in the present work, a glass carbon electrode was developed for the electrochemical detection of RC with good specificity and stability, through modifying the glass carbon electrode (GCE) by polyphenol oxidase (PPO), an NH2-SBA-15 mesoporous material (NH2-SBA-15), L-tyrosine (L-Tyr) and gold nano-particles (AuNPs). After being successively modified by AuNPs, L-Tyr, NH2-SBA-15 and PPO, the constructed PPO/NH2-SBA-15/L-Tyr/AuNPs/GCE was used to discriminate RC from ions and other common micromolecules, which showed a fairly good specificity and stability. The proposed electrochemical detection method features a linear range of from 0.5 to 21.0 μM with a LOD down to 0.15 μM, revealing a better sensitivity than the existing methods. It is worth mentioning that the proposed PPO/NH2-SBA-15/L-Tyr/AuNPs/GCE has been successfully used as an electrochemical probe for the RC assay in domestic sewage.
A synergistic nanocomposite film composed of gold nanourchins (AuNU), oxidised carbon nanohorns (CNH), and chitosan functioned as an electrode modifier in the fabrication of the sensitive lipocalin-2 (LCN-2) aptasensor. The AuNUs/CNH/CS composite increased the surface area and thereby amplified the signal transduction. The amine-terminated LCN-2 aptamer was immobilised through the amide bond formed between the carboxyl group of polyglutamic acid (PGA) and the amine group of aptamer. Interaction of LCN-2 with the aptamer caused conformational changes in the structure of the aptamer. This generated higher conductivity, resulting in increased DPV peak current. The DPV signal increased with increasing concentration of LCN-2, and the change in signal was used for quantitative detection. The proposed aptasensor was able to detect LCN-2 in the linear range of 0.1 – 100.0 pg mL−1, with a low detection limit of 10 fg mL−1. The aptasensor showed high sensitivity, selectivity, reproducibility, and was able to detect LCN-2 in serum samples.
A fluorometric aptasensor based on Escherichia coli O157:H7 (E. coli O157:H7) aptamer labeled aminated carbon quantum dots (NH2-CQDs) and graphene oxide (GO) for the determination of E. coli O157:H7 was developed. In this research, carboxyl group (–COOH) terminated E. coli O157:H7 aptamer was steadily labeled to NH2-CQDs by amidation reaction, and played the role of energy donor and was responsible for chemical recognition. Correspondingly, GO served as an energy acceptor. The introduction of NH2-CQDs not only made the aptamer bond stably through covalent bond, but also significantly enhanced the fluorescence intensity compared with general CQDs. The NH2-CQDs-aptamer is adsorbed on the surface of GO through π-π stacking and hydrophobic interaction. The fluorescence of NH2-CQDs-aptamer was quenched via fluorescence resonance energy transfer (FRET) between NH2-CQDs and GO. After adding E. coli O157:H7, the specific binding affinity between NH2-CQDs-aptamer and E. coli O157:H7 lead to desorption of NH2-CQDs-aptamer from GO, and recovery of the fluorescence intensity of NH2-CQDs-aptamer. Under the optimal conditions, the increased fluorescence intensity showed a good linear relationship to concentrations of E. coli O157:H7 in the range 102 – 107 cells/mL, with a detection limit of 89 cells/mL. Furthermore, the developed method was successfully applied to the determination of E. coli O157:H7 in commercial milk samples.
A photometric method to determine molecular oxygen in water was developed. When manganese(II) is oxidized by oxygen under alkaline conditions, the presence of polyphosphate can prevent precipitation due to a coacervate reaction. The oxidized manganese later dissolves in acid to form a pink Mn(III) species, which has a stable UV/vis spectrum. Monitoring of the oxygen concentration based on the absorbance of the pink Mn(III) species at 517 nm showed a strong correlation with both the Winkler method and an optical sensor. As a result, the present method can measure not only dissolved oxygen, but also fine bubbles oxygen in in the water sample with high reliability (0 – 26 mg dm−3, r2 = 0.9995). During this process, no significant interference from nitrite or metal ions was observed. The accuracy of the measurement was steady at high temperatures of the water samples (≤ 363 K).
In this study, a monolithic organic polymer stationary phase was modified using 18-crown-6-ether for use in capillary ion chromatography. Its use in the separation of inorganic anions was investigated. The monolithic stationary phase was obtained by chemically bonding 2-aminomethyl-18-crown-6-ether to a polymer skeleton comprising glycidyl methacrylate and ethylene glycol dimethacrylate. The optimum level of the loading of 2-aminomethyl-18-crown-6-ether onto the stationary phase was investigated. The resulting stationary phase was used to investigate the influence of the eluent cation, the concentration of the eluent, and the pH of the eluent on the separation of inorganic anions.
In current work, novel functionalized carbon dots have been designed and synthesized by covalently linking dopamine to the surface of S,N co-doped carbon dots (DA-S,N-CDs) for the selective detection of Fe3+ and Fe2+ in water. The as-synthesized DA-S,N-CDs emit blue fluorescence peaked at 470 nm and exhibit excitation-dependent tunable emissions. The tolerance towards pH, salt, and UV irradiation of synthesized carbon dots reveals excellent stability. Upon exposure to Fe3+ or Fe2+, the fluorescence of DA-S,N-CDs was selectively quenched, while other competitive cations did not change significantly. Under the optimal experimental conditions, the fluorescence intensity of DA-S,N-CDs showed a good linear relationship with the concentrations of Fe3+ and Fe2+ (5 – 200 μM for Fe3+ and 5 – 300 μM for Fe2+), and the limit of detection was 2.86 and 2.06 μM, respectively. Furthermore, considering the excellent stability and anti-interference, DA-S,N-CDs have been successfully used for the detection of Fe3+ and Fe2+ in environmental water.
The performance of iodine extraction in the emulsion-flow column was evaluated using an indicator of difficulty in separation, height of transfer unit, HTU and of the number of theoretical plates, Nth. Resulting HTU values ranged from 0.15 to 0.78 m and Nth changed from 0.58 to 1.3. HTU values were formulated in accordance with operating liquid velocities. Despite a 30% margin of error, HTU values were found to be useful in predicting column performance. Observed HTU values were compared with those of conventional extraction columns with or without mechanical agitation. The emulsion-flow column meets the top-level performance of extractors without mechanical agitation, such as packed and spray columns, and performs in the middle range of agitated extractors, although these sacrifice the structure simplicity to assure stable counter-current operation. The advantage of the emulsion-flow column is better HTU values with stable counter-current operation in a simple column structure.
We investigated sputtered nanocarbon films with respect to the effect of suppressing surface oxygen on their electrochemical properties. The nanocarbon film consisted of nanocrystallites with mixed sp2 and sp3 bonds formed by unbalanced magnetron sputtering. Ultraviolet/ozone (UV/O3) irradiation and electrochemical pretreatment (ECP) were conducted to change the surface oxygen concentration of nanocarbon film. X-ray photoelectron spectroscopy (XPS) measurements revealed that nanocarbon films with different amounts of surface oxygen could be prepared. In addition, we observed no significant increase of the surface roughness (Ra) at the angstrom level after treatments, owing to a stable structure containing 40% of sp3 bonds. The electrode characteristics, including the potential window and electrochemical properties for some redox species, such as Ru(NH3)63+/2+, were investigated. Some electrochemical measurements of zinc ions (Zn2+) and hydrogen peroxide (H2O2) showed that the electrochemical reaction was improved by suppressing the surface oxygen. These results clearly indicated that the low surface oxygen concentration plays an important role in these electrochemical reactions.
In the present work, a phenanthroline derivative (2-(2-methoxyphenyl)-4-phenyl-1,10-phenanthroline, MPP), as a fluorescent probe, was synthesized to realize a rapid, simple and sensitive detection of silver(I). The detection conditions of Ag+ were optimized. This fluorescent probe has the advantages of a fast reaction time, a wide pH applicable range, and a low detection limit, exhibiting a good linear response between the fluorescence intensity and the concentration in the range of 0.05 – 1.5 μmol/L for Ag+. The detection limit is as low as 3.38 × 10−8 mol/L (S/N = 3). This probe had been used to detect Ag+ in real samples, and the recovery efficiency of spiked Ag+ had been also tested. The recovery efficiency is satisfactory, ranging from 92.0 to 105.4%. Therefore, this fluorescent probe should provide a new choice for the quantitative detection of silver ions in environmental water samples.
Batchwise equilibrium study was carried out on the retention of nonpolar and polar organic compounds to octadecylsilyl (ODS) silicas of different properties at atmospheric pressure. While nonpolar compounds were retained only by distribution on the ODS phase, polar compounds were retained by both distribution and Langmuir-type adsorption on residual silanol. Retention on ODS silica with more silanol proceeded at a higher rate than retention on ODS silica with less silanol and was reversible on this solid phase extraction time-scale. An increase in surface density of ODS decreased the distribution constant, due to a decrease in fraction of ODS functioning as an extracting medium and also decreased the saturated adsorption amount, due to reductions of the residual silanol and the functioning ODS. The ODS silica with the lowest ODS density showed a distribution constant 31 times higher and a saturated adsorption amount 27 times higher than the ODS silica with the highest ODS density. On the other hand, because the interaction between the organic part and the ODS group introduced at higher density is strengthened, the adsorption constant is increased by about 5 times compared to the low density ODS silica. The electronic effects of substituents to nitrogen- and oxygen-containing compounds on retention were discussed. In conclusion, ODS silica with an appreciable amount of residual silanol is superior for solid phase extraction.
A liquid-membrane type nitrate-selective electrode was improved to lower the influence of contaminants by modifying its inner electrode system from Ag | AgCl | Cl− to Ag | Ag+. The NO3−-selective electrode displayed a linear response to the concentration of NO3− with a Nernstian slope of –53 ± 1 mV decade−1, in the concentration region between 10−5 and 2 mol dm−3 (M). The NO3− detection limit was about 10−5 M. The electrochemical response of this electrode was stable for more than 30 days. The deterioration in responding characteristics due to the coexistence of Cl− was suppressed by use of the Ag | Ag+ redox couple in the absence of Cl− inside the NO3−-selective electrode.
A modified electrode was developed by immobilizing poly(azure A) (pAA) onto the surface of a glassy carbon electrode via the electropolymerization of azure A (AA). The pAA immobilized on the electrode exhibited redox response during cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The redox reaction obeyed the Nernst equation because of the involvement of H+ ions. In addition, the peak potential was shifted according to the solution pH. The shifts of the oxidation peak potential could be more easily observed using DPV than when using CV, indicating that the developed electrode could be useful as a pH sensor. This pH measurement method can be successfully applied in the pH range of 1 to 10 and can be successfully repeated more than 50 times.
Nanoelectrospray ionization (nESI) mass spectrometry (MS) is an ideal detection method for microfluidic chips, and its performances depend on nESI emitters. However, the fabrication of monolithic nESI emitters in chips was difficult. Herein, we propose a three-dimensional (3D) printing method to develop a microfluidic nanoelectrospray ionization source (NIS), composed of a nESI emitter and other components. Firstly, the NIS was compatible with a 50 – 500 nL min−1 nanoflows by imposing 3D hydrodynamic focusing to compensate for the total flow rate, achieving a 7.2% best relative standard deviation in the total ion current (TIC) profiles. Additionally, it was applied to probe thirteen organic chemicals, insulin, and lysozyme with adequate signal-to-noise ratios and an accuracy of m/z between 9.02 × 10−1 and 1.48 × 103 ppm. Finally, the NIS achieved comparable limits of detection compared with its commercial counterpart. Considering the standardized preparation of NIS, it would be a potential option to develop 3D-printed customized Chip-MS platforms.
Herein, we designed a label-free fluorescent aptasensor based on triple-helix DNA and G-quadruplex for carbohydrate antigen (CA15-3) detection. The triplex-helix structure can be formed with inserted G-rich DNA (IG) and aptamer DNA (Apt), which like a “lock” to lock the G-rich sequences. The CA15-3 was the “key”, which specifically combined with aptamer sequences of Apt, resulting in liberating IG from the triplex-helix “lock”. Then, the G-rich sequences of IG were formed into G-quadruplex and specifically interacted with N-methylmesoporphyrin IX (NMM), which greatly enhanced the fluorescence of the solution. However, when the “key” did not exist, the “lock” was fastened and fluorescence intensity did not change. With this proposed method, the concentration of CA15-3 can be effectively detected from 0.01 to 5 U mL−1 with a detection limit (LOD) of 0.01 U mL−1. Furthermore, this proposed biosensor can be applied to spiked human serum with great precision and reproducibility.
A detection system consisting of a photothermal heterodyne interferometer (PHI) combined with semi-micro HPLC (high-performance liquid chromatography) has been designed and investigated. An ultraviolet (UV) or deep-UV laser emitting at 375 or 213 nm, respectively, was used for the excitation of nitro-polycyclic aromatic hydrocarbons (NPAHs) and amino acids. A photothermally induced change in the refractive index of the solvent causes an optical phase difference between two arms of the interferometer, one beam passing through the photoexcited region and another used as a reference, which was sensitively detected with the PHI. The separation and detection of NPAHs and amino acids were successfully demonstrated via semi-micro HPLC with the PHI and a UV detector. The detection limits of the UV-excitation PHI for NPAHs were 1.2 – 5.2 times better than that of the commercial UV detector, although the first demonstration of deep-UV excitation suffered from significant baseline fluctuation.
Relative molar sensitivity (RMS) determined using quantitative 1H NMR and HPLC with a refractive index (RI) detector was applied as a specific value for quantifying the levels of heptaoxyethylene dodecyl ether (HOEDE), a typical non-ionic surfactant, in methanol solutions. RMS was robust against changes of the analytical conditions (i.e., RI cell temperature, acetonitrile content in the mobile phase, HPLC system). Furthermore, the obtained HOEDE concentrations using a previously evaluated RMS were comparable to those obtained using a reference method for over 1 year.