Electrochemical fabrication of reduced MoS2-based portable molecular imprinting nanoprobe for selective SERS determination of theophylline.

A new portable molecular imprinting polymer (MIP)-SERS nanoprobe is fabricated by a convenient electrochemical method. Single-layered MoS2 is electrochemically reduced on a screen-printed electrode as the scaffold. Functional monomers o-phenylenediamine (oPD), template theophylline (THP), and SERS-active Au nanoparticles (AuNPs) are then one-step electropolymerized on the scaffold. The morphology of the nanoprobe is found to be a three-dimensional and porous structure. The abundant AuNPs with the size of 45~50 nm are trapped within the growing MIP instead of being confined to the surface. The thickness of MIP film is calculated to 25.1 nm. The nanoprobe displays a strong SERS effect for THP using 532 nm as excitation wavelength with a detection limit (LOD) of 0.01 nM. The SERS peak intensity at 1487 cm-1 increases linearly with the concentration of THP in the range 0.1 nM to 0.1 mM. After the template is removed, the imprint-removed nanoprobe is generated for selective binding of THP. The re-binding kinetics study implies the portable MIP-SERS nanoprobe can reach the adsorption equilibrium within 8 min. This nanoprobe exhibits low SERS interference for structural analogues theobromine (THB) and caffeine (CAF). The nanoprobe was employed to THP determination in tea drink samples, with recoveries ranging from 99.0 to 102.0% and relative standard deviations of < 5.0%. Graphical abstractSchematic representation of a portable molecular imprinting SERS nanoprobe used for selective and sensitive theophylline recognition. The nanoprobe is fabricated by one-step electropolymerized o-phenylenediamine (oPD), theophylline, and electroreduced Au nanoparticles (AuNPs) on reduced MoS2 (rMoS2) modified screen-printed electrode (SPE).

Humic acids-based one-step fabrication of SERS substrates for detection of polycyclic aromatic hydrocarbons.

A facile one-step approach to fabricate substrates for surface-enhanced Raman scattering (SERS) detection of polycyclic aromatic hydrocarbons (PAHs) was explored by reduction of silver nitrate with humic acids (HAs). This simple process readily delivers silver nanoparticles (Ag NPs) decorated with HAs (HAs-Ag NPs), and an average diameter of 50 nm. More importantly, it compares favorably to Ag NPs prepared by the usual sodium citrate method, HAs-Ag NPs show excellent SERS activity for PAHs and display a remarkable capacity to absorb aromatic molecules through presumed π-π stacking interactions. Furthermore, the HAs-Ag NPs displayed good SERS stability, possibly due to the fact that HAs form loose coils or networks around the nanoparticles thus preventing aggregation. The investigation of qualitative and quantitative detection of PAHs on HAs-Ag NPs indicate that different PAHs can be distinguished easily from their discriminant SERS peaks, and the SERS responses exhibited a linear dependence on PAH concentrations over two orders of magnitude, with tens of nM detection limits. In addition, the HAs-Ag NPs performed well in the multicomponent analysis of PAH mixtures by the SERS technique without pre-separation.

A novel screen-printed electrode array for rapid high-throughput detection.

A novel multi-channel electrode array sensing device was fabricated by screen-printing techniques using 96-well plate as the template. To confirm its practical value, we developed a one-step preparation of multi-walled carbon nanotubes (MWCNTs) doped electrode array by an ink containing MWCNTs, which was applied to the simultaneous detection of a variety of biological samples and environmental pollutants. Results demonstrated that the designed sensing device could carry out the multiple measurements of different analytes at the same time, while MWCNTs enhanced the electrocatalytic activity of electrodes toward electroactive molecules. The required amount of each sample was only ∼200 µL. Moreover, the excellent differential pulse voltammetric (DPV) response toward dopamine, hydroquinone and catechol was obtained and the detection limits was determined to be 0.337, 0.289 and 0.369 µM, respectively. Comparing it with the traditional screen-printed electrode (SPE), this sensing device possesses the advantages of high-throughput, fast electron transfer rate for electrodes, short-time analysis and low sample consumption.

Cloning, expression and characterization of trehalose-6-phosphate phosphatase from a psychrotrophic bacterium, Arthrobacter strain A3.

A trehalose-6-phosphate phosphatase (TPP) gene, otsB, from a psychrotrophic bacterium, Arthrobacter strain A3, was identified. The product of this otsB gene is 266 amino acids in length with a calculated molecular weight of 27,873 Da. The protein was expressed in Escherichia coli and purified to apparent homogeneity. The purified recombinant TPP catalyzed the dephosphorylation of trehalose-6-phosphate to form trehalose and showed a broad optimum pH range from 5.0 to 7.5. This enzyme also showed an absolute requirement for Mg(2+) or Co(2+) for catalytic activity. The recombinant TPP had a maximum activity at 30 °C and maintained activity over a temperature range of 4-30 °C. TPP was generally heat-labile, losing 70 % of its activity when subjected to heat treatment at 50 °C for 6 min. Kinetic analysis of the Arthrobacter strain A3 TPP showed ~tenfold lower K (m) values when compared with values derived from other bacterial TPP enzymes. The highest k (cat)/K (m) value was 37.5 mM(-1) s(-1) (repeated three times), which is much higher than values published for mesophilic E. coli TPP, indicating that the Arthrobacter strain A3 TPP possessed excellent catalytic activity at low temperatures. Accordingly, these characteristics suggest that the TPP from the Arthrobacter strain A3 is a new cold-adapted enzyme. In addition, this is the first report characterizing the enzymatic properties of a TPP from a psychrotrophic organism.

Types of Descemet Membrane Detachment After Ocular Surface Burns: The Factor Long Been Ignored.

PURPOSE: The aim of this study was to explore types of Descemet membrane detachment (DMD) after ocular surface burns by anterior segment optical coherence tomography. METHODS: This is a pilot, case series, observational study. Patients with DMD after ocular surface burns were enrolled. Ophthalmologic examinations were performed in all patients including slit-lamp photography and anterior segment optical coherence tomography. RESULTS: Three types of DMDs in 9 eyes of 9 patients with ocular surface burns were identified depending on the detachment components involved with the pre-Descemet layer (PDL). Type A was referred as a taut chord that the PDL and Descemet membrane (DM) detached simultaneously but were remained attached to each other, while type B was identified as a wavy line separated from the stroma by a dark slit that demonstrated the detachment of DM from the PDL and stroma. Type C was defined as the DM detached with or without PDL but they were separated from each other. We found that DM and PDL were detached simultaneously in most condition, with type A in 4 cases, type C in 5 cases, and type B in only 1 case. CONCLUSIONS: Our study demonstrated 3 types of DMDs after ocular surface burns and revealed that the limbal involvement and retrocorneal exudations may give clues to DMD in the corresponding areas. DMDs may be neglected for long in patients with extensive limbal involvement in early stages and also play an important role in unstable ocular surface condition until the late stages of conjunctivalization after ocular surface burns.

A wearable screen-printed SERS array sensor on fire-retardant fibre gloves for on-site environmental emergency monitoring.

Glove-based wearable sensors can offer the potential ability to a fast and on-site environmental threat assessment, which is crucial for timely and informed incident management. In this study, an on-demand surface-enhanced Raman scattering (SERS) array sensor has been patterned on fire-retardant fibre gloves via the screen-printing technique in large batches. The screen-printed ink contains one-pot synthesized silver nanoparticle and molybdenum disulfide nanocomposite (Ag/MoS2), and polyanionic cellulose (PAC) as a new adhesive agent. Rhodamine 6G (R6G) was employed as an initial probe molecule to systematically evaluate the performance of the resulting sensor. The results suggest that the fabricated fire-retardant screen-printed SERS array sensor displays high reproducibility and stability at 250 °C, with the lower detection limit of 10-13 M for R6G. The spot-to-spot SERS signals show that the intensity variation was less than 10%. Besides, the SERS signals can be maintained over 7 weeks. Further investigation was then successfully carried out to detect polycyclic aromatic hydrocarbons (PAHs), which are commonly used as flammable chemicals. In our perception, this wearable fire-retardant screen-printed SERS array sensor would be an ideal candidate for practical on-site environmental emergency monitoring due to its fire-retardant capability and timely measurement on a portable carrier.

Regulation of expression of trehalose-6-phosphate synthase during cold shock in Arthrobacter strain A3.

Trehalose is a chemical chaperone known to protect a variety of organisms against cold stress. Members of the genus Arthrobacter, which belongs to the Actinomycetales group, exhibit strong resistance to stress conditions, but exactly how trehalose synthesis is regulated in conditions of cold stress is still unknown. Here, we report that Arthrobacter strain A3, which was isolated from the alpine permafrost, has only two trehalose synthesis pathways (OtsA/B and TreS), while other Arthrobacter spp. have three. Mutants and immunoblot analyses indicate that trehalose is mainly synthesized via OtsA at low temperatures in Arthrobacter strain A3. Therefore, we have focused on the regulation of OtsA expression during cold shock. The results indicated that both low temperature and accumulation of trehalose can inhibit OtsA expression. The elongation factor Tu, which binds to OtsA, stabilizes the expression of OtsA in the cold.

The catalytic efficiency of trehalose-6-phosphate synthase is effected by the N-loop at low temperatures.

The enzyme OtsA (trehalose-6-phosphate synthase) is ubiquitous in both prokaryotic and eukaryotic organisms, where it plays a critical role in stress resistance and glucose metabolism. Here, we cloned the otsA gene from Arthrobacter sp. Cjts, and expressed and then purified the recombinant proteins. Enzyme activity analysis indicated that the high catalytic efficiency of OtsA from Arthrobacter sp. Cjts resulted from the high affinity of the enzyme for uridine 5'-diphosphoglucose (UDP-Glc) at low temperatures. We also confirmed that the N-loop sequence of OtsA has a large effect on its affinity for UDP-Glc. Sequence analysis indicated that the flexibility of the N-loop may be directly related to the catalytic efficiency of OtsA at low temperatures.

Efficacy and safety of computed tomography-guided 125I brachytherapy for lymph node metastatic from hepatocellular carcinoma.

PURPOSE: A survival benefit may be associated with the positive control of extrahepatic lymph node metastasis (LNM) of hepatocellular carcinoma (HCC). However, no standard treatment exists. The aim of this study was to evaluate the safety and efficacy of iodine-125 (125I) brachytherapy (BT) of LNM of HCC, especially in patients with multiple lymph nodules or repeated lymph node recurrence. MATERIALS AND METHODS: From June 2007 to July 2016, clinical and imaging data of 22 patients were collected at our center. According to the treatment planning system, 37 BT targets were treated by seed implantation with computed tomography (CT)-guidance. The radioactive treatment-related adverse events and surgical complications were recorded. The BT target therapeutic response was evaluated by the RECIST. The median survival time and rates were evaluated by the Kaplan-Meier method. RESULTS: Twenty-two patients were enrolled (median age: 48 years; 90.9% males), and 58 lymph node areas were diagnosed as metastatic. The incidence of LNM was high in porta hepatis (33.9%) and right para-aortic nodes (14.2%), and lower incidence rates were observed in other areas. The median imaging follow-up time was 12 months (inter-quartile range 5.5-20.5), the complete response was 29, the partial response was 5, the stable disease was 2, the progressive disease was 1, and the local response rate was 91.8%. The median survival time from the beginning of BT was 25 months. The 1, 2, and 3-year overall survival rates were 64.3%, 43.4%, and 27.1%, respectively, and the 5-year overall survival rate from the time of HCC diagnosis was 31.1%. No BT-induced acute morbidity according to the Radiation Therapy Oncology Group criteria was reported. After 5.5 months, one patient diagnosed with a duodenal ulcer underwent gastroduodenoscopy. The surgical complications included mild pancreatitis in 3 patients and stomach bleeding and pneumothorax in 1 patient. CONCLUSION: CT-guided 125I BT treatment of LNM of HCC presented good local control rates and controllable complications. It is a safe and effective palliative treatment for patients with LNM of HCC. Further study is needed to evaluate its long-term safety and efficacy.

Label-free in-situ monitoring of protein tyrosine nitration in blood by surface-enhanced Raman spectroscopy.

A novel label-free method for the in-situ monitoring of protein tyrosine nitration (PTN) was explored based on surface-enhanced Raman spectroscopy (SERS). Benefiting from the relative weak binding ability of sulfate to silver surface, the Raman signals of nitrated peptides were boosted well with sulfate-aggregated silver nanoparticles (Ag NPs). The distinction of the SERS spectra between non-nitrated peptides and nitrated peptides was obtained by directly comparing SERS bands at 330-400cm(-1), allowing the rapid identification of PTN. Furthermore, without any pretreatments, the established method was successfully applied in the rapid in-situ dynamic monitoring of the mimic hemin-catalyzed PTN process in synthetic peptide, bovine serum albumin (BSA), and original human blood serum samples. The results indicated that the proposed approach could be a promising in-situ label-free tool for observing PTN process, which may be quite helpful to deeply understand the mechanism of post-translation modification.

Rapid and sensitive in-situ detection of polar antibiotics in water using a disposable Ag-graphene sensor based on electrophoretic preconcentration and surface-enhanced Raman spectroscopy.

A disposable Ag-graphene sensor was developed for rapid and sensitive in-situ detection of polar antibiotics in water using electrophoretic preconcentration (EP) and surface-enhanced Raman spectroscopy (SERS). The Ag-graphene sensor was fabricated by depositing Ag-graphene nanocomposites synthesized through a facile one-pot method on the disposable screen-printed electrodes (SPEs) and characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). SERS properties and detection applicability of the developed sensor were systematically investigated. It is shown that the polar antibiotics can be selectively adsorbed on the oppositely charged sensors after applying different potentials during the EP procedure, and the SERS signals of antibiotics with an effective amplification can be achieved with proper time of preconcentration. Moreover, the Ag-graphene sensor could facilitate the molecule adsorption through weak π-π interactions between graphene and antibiotics, further improving the sensitivity of SERS detection. Under the optimum EP conditions, the representative SERS spectra of a mixed solution containing four different antibiotics can be obtained within 10 min, and each antibiotic is easily distinguished by its characteristic peaks with a sub-nM detection level. The results demonstrate that the proposed disposable Ag-graphene sensor based on EP-SERS can be used for rapid and sensitive in-situ detection of polar antibiotics in aqueous samples without a pre-separation step.

Fabrication of bimetallic microfluidic surface-enhanced Raman scattering sensors on paper by screen printing.

Au-Ag bimetallic microfluidic, dumbbell-shaped, surface enhanced Raman scattering (SERS) sensors were fabricated on cellulose paper by screen printing. These printed sensors rely on a sample droplet injection zone, and a SERS detection zone at either end of the dumbbell motif, fabricated by printing silver nanoparticles (Ag NPs) and gold nanoparticles (Au NPs) successively with microscale precision. The microfluidic channel was patterned using an insulating ink to connect these two zones and form a hydrophobic circuit. Owing to capillary action of paper in the millimeter-sized channels, the sensor could enable self-filtering of fluids to remove suspended particles within wastewater without pumping. This sensor also allows sensitive SERS detection, due to advantageous combination of the strong surface enhancement of Ag NPs and excellent chemical stability of Au NPs. The SERS performance of the sensors was investigated by employing the probe rhodamine 6G, a limit of detection (LOD) of 1.1×10(-13)M and an enhancement factor of 8.6×10(6) could be achieved. Moreover, the dumbbell-shaped bimetallic sensors exhibited good stability with SERS performance being maintained over 14 weeks in air, and high reproducibility with less than 15% variation in spot-to-spot SERS intensity. Using these dumbbell-shaped bimetallic sensors, substituted aromatic pollutants in wastewater samples could be quantitatively analyzed, which demonstrated their excellent capability for rapid trace pollutant detection in wastewater samples in the field without pre-separation.

Recent developments and applications of screen-printed electrodes in environmental assays--a review.

Screen-printed electrodes (SPEs), which are used as economical electrochemical substrates, have gone through significant improvements over the past few decades with respect to both their format and their printing materials. Because of their advantageous material properties, such as disposability, simplicity, and rapid responses, SPEs have been successfully utilised for the rapid in situ analysis of environmental pollutants. This critical review describes the basic fabrication principles, the configuration designs of SPEs and the hybrid analytical techniques based on SPEs. We mainly overview the electrochemical applications of SPEs in environmental analysis over the past 3 years, including the determination of organic compounds, heavy metals and gas pollutants.

Disposable biosensor based on graphene oxide conjugated with tyrosinase assembled gold nanoparticles.

A highly efficient enzyme-based screen printed electrode (SPE) was obtained by using covalent attachment between 1-pyrenebutanoic acid, succinimidyl ester (PASE) adsorbing on the graphene oxide (GO) sheets and amines of tyrosinase-protected gold nanoparticles (Tyr-Au). Herein, the bi-functional molecule PASE was assembled onto GO sheets. Subsequently, the Tyr-Au was immobilized on the PASE-GO sheets forming a biocompatible nanocomposite, which was further coated onto the working electrode surface of the SPE. The characterization of obtained nanocomposite and modified SPE surface was investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Attributing to the synergistic effect of GO-Au integration and the good biocompatibility of the hybrid-material, the fabricated disposable biosensor (Tyr-Au/PASE-GO/SPE) exhibited a rapid amperometric response (less than 6s) with a high sensitivity and good storage stability for monitoring catechol. This method shows a good linearity in the range from 8.3×10(-8) to 2.3×10(-5) M for catechol with a squared correlation coefficient of 0.9980, a quantitation limit of 8.2×10(-8) M (S/N=10) and a detection limit of 2.4×10(-8) M (S/N=3). The Michaelis-Menten constant was measured to be 0.027 mM. This disposable tyrosinase biosensor could offer a great potential for rapid, cost-effective and on-field analysis of phenolic compounds.

[Investigation on simultaneous determination of dihydroxybenzene isomers in water samples using multi-walled carbon nanotube modified screen-printed electrode].

A disposable electrode, multi-walled carbon nanotube modified screen printed electrode (MWCNT/SPE), had been fabricated using screen printing technology and drop-coating method to determine dihydroxybenzene isomers (hydroquinone, catechol and resorcinol). The cyclic voltammetry behavior of dihydroxybenzene isomers had been investigated with the MWCNT/SPE. The results reveal that MWCNT/SPE, which shows a strong electrocatalytic activity for the oxidation of dihydroxybenzenes, can entirely separate the oxidation peaks of them. According to differential pulse voltammetry tests, the peak currents of dihydroxybenzene isomers are linear to their concentrations at the range of 8.20 x 10(-6) -1.00 x 10(-3), 8.20 x 10(-6) -1.00 x 10(-3) and 1.64 x 10(-5) -1.16 x 10(-3) mol x L(-1), with the detection limits of 4.34 x 10(-6), 3.42 x 10(-6) and 6.70 x 10(-6) mol x L(-1) for hydroquinone, catechol and resorcinol, respectively. For the determination of dihydroxybenzene isomers in water samples, the value of recovery found by standard addition method was in the range of 96.2%-104.9%. These results indicate MWCNT/SPE can be applied to rapid in-situ determination of dihydroxybenzenes-polluted water samples.

Highly selective in situ metal ion determination by hybrid electrochemical "adsorption-desorption" and colorimetric methods.

A novel and facile hybrid analytical method coupling electrochemical "adsorption-desorption" and colorimetric analyses was developed to detect heavy metal ions in turbid water samples. The target metal ions were deposited onto an electrode inserted into the original sample, which was referred to as the "adsorption" process. After changing the medium, the concentrated target metal ions were dissolved in a new, clean buffer (blank buffer), which was referred to as the "desorption" process. The concentrations of the target metal ions were measured by colorimetric analyses after the addition of specific indicator amounts. We demonstrated the applicability of this method by detecting Cd(2+), Pb(2+) and Cu(2+) with co-depositing Bi(3+) on portable screen-printed electrodes (SPEs). A good correlation (correlation coefficient of R=0.997) was observed between concentrations ranging from 1 to 200 µM and absorbance values. After the multiple "desorption" process, the even better detection limits as low as 10, 10 and 100 nM were achieved for Cd(2+), Pb(2+) and Cu(2+), respectively. The practicality of this hybrid method was confirmed by the detection of Cd(2+), Pb(2+) and Cu(2+) in wastewater samples, and these results were in agreement with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall, this hybrid method provides a simple, selective and effective technique for environmental pollutant analyses.