A core-molecule-shell Au@PATP@Ag nanorod for nicotine detection based on surface-enhanced Raman scattering technology.

Nicotine is an addictive substance often found in tobacco and cigarette smoke and excessive exposure to it can cause various diseases. Herein, core-molecule-shell gold/4-aminothiophenol/silver nanorods (Au@PATP@Ag NRs) were prepared for quantitative detection of nicotine by using surface-enhanced Raman scattering (SERS) technology. The obtained Au@PATP@Ag NRs showed an outstanding SERS effect due to the plasticity of their morphology and the bimetallic synergistic effect between the excellent stability of Au and the highly enhanced effect of Ag. The Au@PATP@Ag NRs substrate exhibited an extremely high enhancement factor (EF) of 2.17 × 107. In addition, in-situ synthesized PATP was used as an internal standard to correct signal fluctuation and improve the reliability of quantitative nicotine detection. A wide linear dynamic range from 10-8 to 10-3 M was obtained and an ultra-low limit of detection (LOD) was about 3.12 × 10-9 M, which was superior to most of previously reported methods. This work has also been used for determining nicotine content in cigarettes and simulated environmental tobacco smoke by using a portable device. These results indicated that the developed SERS method had many potential applications in the quantitative determination of nicotine in real tobacco samples.

SlZF3 regulates tomato plant height by directly repressing SlGA20ox4 in the gibberellic acid biosynthesis pathway.

Plant height is an important target trait for crop genetic improvement. Our previous work has identified a salt-tolerant C2H2 zinc finger, SlZF3, and its overexpression lines also showed a semi-dwarf phenotype, but the molecular mechanism remains to be elucidated. Here, we characterized the dwarf phenotype in detail. The dwarfism is caused by a decrease in stem internode cell elongation and deficiency of bioactive gibberellic acids (GAs), and can be rescued by exogenous GA3 treatment. Gene expression assays detected reduced expression of genes in the GA biosynthesis pathway of the overexpression lines, including SlGA20ox4. Several protein-DNA interaction methods confirmed that SlZF3 can directly bind to the SlGA20ox4 promoter and inhibit its expression, and the interaction can also occur for SlKS and SlKO. Overexpression of SlGA20ox4 in the SlZF3-overexpressing line can recover the dwarf phenotype. Therefore, SlZF3 regulates plant height by directly repressing genes in the tomato GA biosynthesis pathway.

Care practices and short-term clinical outcomes of very low birth weight infants in Yangtze River Delta in China.

BACKGROUND: Intensive care is of great significance for very low birth weight infants (VLBWI). The Yangtze River Delta is the most ecomonically developed area in China. However, there are few data on the care practices and survival of VLBWI in this region. OBJECTIVES: To investigate the prevalence, care practices and motality of VLBWI in Yangtze River Delta in China. METHODS: A multi-center retrospective investigation study was conducted at five tertiary hospitals within the Yangtze River Delta in China from January to December 2017. Clinical data included the general characteristics of the infants and the mothers, clinical prognosis, care practices in NICUs was collected by trained research members. RESULTS: During the study period, 1059 VLBWIs were included. Infants with birth weight < 750 g, 750-1000 g, 1000-1250 g and 1250-1500 g accounted for 2.3, 14.9, 34.8 and 47.8%, respectively. Premature rupture of membranes (17.8%) was the main cause of premature delivery. The catheterization rates of umbilical vein catheterization (UVC) and peripherally inserted central catheter (PICC) were 25.0 and 64.4%, respectively. The duration of parenteral nutrition was 27.0 ± 19.5 d, the meantime of feeding tube indwelling was 36.2 ± 24.2 d. The corrected gestational age of the infants who reached full oral feeding was 35.8 ± 2.7 weeks. The breast feeding rate in the investigated infants was 61.9%. The mortality rate of preterm infants was 3.4%. The incidence of main complications BPD, PDA, ROP, NEC and sepsis were 24.9, 29.9, 21.7, 9.4 and 13.3% respectively. CONCLUSIONS: Maternal and infant care practices need to be improved in the very preterm births. This study provides a baseline for the improvement in the further study.

Systematic Analysis of the Grafting-Related Glucanase-Encoding GH9 Family Genes in Pepper, Tomato and Tobacco.

Grafting is an important agricultural practice to control soil-borne diseases, alleviate continuous cropping problems and improve stress tolerance in vegetable industry, but it is relatively less applied in pepper production. A recent study has revealed the key roles of ß-1, 4-glucanase in graft survival. We speculated that the GH9 family gene encoding glucanase may be involved in the obstacles of pepper grafting. Therefore, we performed a systematic analysis of the GH9 family in pepper, tomato and tobacco. A total of 25, 24 and 42 GH9 genes were identified from these three species. Compared with the orthologues of other solanaceous crops, the deduced pepper GH9B3 protein lacks a conserved motif (Motif 5). Promoter cis-element analysis revealed that a wound-responsive element exists in the promoter of tobacco NbGH9B3, but it is absent in the GH9B3 promoter of most solanaceous crops. The auxin-responsive related element is absent in CaGH9B3 promoter, but it presents in the promoter of tobacco, tomato, potato and petunia GH9B3. Tissue and induction expression profiles indicated that GH9 family genes are functionally differentiated. Nine GH9 genes, including CaGH9B3, were detected expressing in pepper stem. The expression patterns of NbGH9B3 and CaGH9B3 in grafting were different in our test condition, with obvious induction in tobacco but repression in pepper. Furthermore, weighted correlation network analysis (WGCNA) revealed 58 transcription factor genes highly co-expressed with NbGH9B3. Eight WRKY binding sites were detected in the promoter of NbGH9B3, and several NbWRKYs were highly co-expressed with NbGH9B3. In conclusion, the missing of Motif 5 in CaGH9B3, and lacking of wound- and auxin-responsive elements in the gene promoter are the potential causes of grafting-related problems in pepper. WRKY family transcription factors could be important regulator of NbGH9B3 in tobacco grafting. Our analysis points out the putative regulators of NbGH9B3, which would be helpful to the functional validation and the study of signal pathways related to grafting in the future.

Genetic mutation of TRPV2 induces anxiety by decreasing GABA-B R2 expression in hippocampus.

Transient receptor potential vanillic acid 2 (TRPV2) are well recognized for their contributions to neuronal development, cardiac function, immunity and cancer. However, the precise roles for this thermo TRPchannels in neurological disorder remain unknown. In this study, we employed the CRISPR/Cas9 system to generate genetic mutations of TRPV2. Genetic mutation of TRPV2 resulted in autistic-like phenotypes in mice accompanied with the disordered electrical signals recorded by multi-channels in vivo. To determine possible molecular mechanisms, western blotting was further used to assess the possible involvement of several autism-related proteins. The significantly decreased expression of the R2 subunit of the GABA-B receptor in the hippocampus was observed. Together, our findings suggest that genetic mutation of TRPV2 induces autism-like behavior, results in decreased expression of the R2 subunit of the GABA-B receptor.

Cancer Cell-Membrane Biomimetic Boron Nitride Nanospheres for Targeted Cancer Therapy.

PURPOSE: Nanomaterial-based drug-delivery systems allowing for effective targeted delivery of smallmolecule chemodrugs to tumors have revolutionized cancer therapy. Recently, as novel nanomaterials with outstanding physicochemical properties, boron nitride nanospheres (BNs) have emerged as a promising candidate for drug delivery. However, poor dispersity and lack of tumor targeting severely limit further applications. In this study, cancer cell-membrane biomimetic BNs were designed for targeted anticancer drug delivery. METHODS: Cell membrane extracted from HeLa cells (HM) was used to encapsulate BNs by physical extrusion. Doxorubicin (Dox) was loaded onto HM-BNs as a model drug. RESULTS: The cell-membrane coating endowed the BNs with excellent dispersibility and cytocompatibility. The drug-release profile showed that the Dox@HM-BNs responded to acid pH, resulting in rapid Dox release. Enhanced cellular uptake of Dox@HM-BNs by HeLa cells was revealed because of the homologous targeting of cancer-cell membranes. CCK8 and live/dead assays showed that Dox@HM-BNs had stronger cytotoxicity against HeLa cells, due to self-selective cellular uptake. Finally, antitumor investigation using the HeLa tumor model demonstrated that Dox@HM-BNs possessed much more efficient tumor inhibition than free Dox or Dox@BNs. CONCLUSION: These findings indicate that the newly developed HM-BNs are promising as an efficient tumor-selective drug-delivery vehicle for tumor therapy.

Fluorescent Assay of FEN1 Activity with Nicking Enzyme-Assisted Signal Amplification Based on ZIF-8 for Imaging in Living Cells.

Flap endonuclease 1 (FEN1) participates in both DNA replication and repair to maintain the stability and integrity of the genome. As a potential tumor marker, detecting FEN1 activity could be an effective strategy for cancer diagnosis. In this work, a fluorescence assay was developed for sensitive detection of FEN1 using biomineralized metal-organic framework nanoparticles (ZIF-8 NPs) to codeliver the encapsulated proteins and DNA probes to living cells. After uptake into cells, the biomineralized ZIF-8 NPs were biodegraded to release proteins and DNA probes under an acid environment. In the presence of FEN1, the cleaved flap triggered by FEN1 hybridized with a hairpin probe to fabricate a double-stranded DNA structure which had a cleavage site of the nicking enzyme, causing the fluorophore to move away from the quencher. Assisting the nicking enzyme, an amplified fluorescence signal was obtained after several recycling. Confocal imaging indicated that this fluorescence assay could distinguish cancer cells from normal cells. Therefore, this strategy would contribute to the prediction and diagnosis in early-stage cancer.

Identification of a ß-Arrestin 2 Mutation Related to Autism by Whole-Exome Sequencing.

Autism spectrum disorder (ASD) is a complex neurological disease characterized by impaired social communication and interaction skills, rigid behavior, decreased interest, and repetitive activities. The disease has a high degree of genetic heterogeneity, and the genetic cause of ASD in many autistic individuals is currently unclear. In this study, we report a patient with ASD whose clinical features included social interaction disorder, communication disorder, and repetitive behavior. We examined the patient's genetic variation using whole-exome sequencing technology and found new de novo mutations. After analysis and evaluation, ARRB2 was identified as a candidate gene. To study the potential contribution of the ARRB2 gene to the human brain development and function, we first evaluated the expression profile of this gene in different brain regions and developmental stages. Then, we used weighted gene coexpression network analysis to analyze the associations between ARRB2 and ASD risk genes. Additionally, the spatial conformation and stability of the ARRB2 wild type and mutant proteins were examined by simulations. Then, we further established a mouse model of ASD. The results showed abnormal ARRB2 expression in the mouse ASD model. Our study showed that ARRB2 may be a risk gene for ASD, but the contribution of de novo ARRB2 mutations to ASD is unclear. This information will provide references for the etiology of ASD and aid in the mechanism-based drug development and treatment.

Deletion of Kv10.2 Causes Abnormal Dendritic Arborization and Epilepsy Susceptibility.

The abnormal function of the voltage-gated potassium channel Kv10.2 can induce epilepsy. However, the physiological function of Kv10.2 in the central nervous system remains unclear. In this study, we found that Kv10.2 knockout (KO) increased the complexity of neurons in the CA3 subarea of hippocampus. Kv10.2 KO led to enlarged somata, elongated dendritic length, and increased the number of dendritic tips in cultured rat hippocampus neurons. Kv10.2 KO also increased Synapsin I and PSD95 protein density in cultured rat hippocampal neurons. Whole cell patch-clamp recordings of brain slices in the CA3 subarea of hippocampus revealed that Kv10.2 KO increased the amplitude of spontaneous excitatory postsynaptic currents (sEPSC) and miniature excitatory postsynaptic currents (mEPSC), depolarized the resting membrane potential and increased the action potential firing, reduced the rheobase and increased the input resistance, which results in enhanced neuronal excitability. Furthermore, we made electroencephalogram (EEG) recordings of brain activity in freely moving rats before and after inducing seizures by pentylenetetrazole (PTZ) injection. Kv10.2 KO rats dramatically increased the EEG amplitude during epilepsy. Behavioral observation after seizure induction revealed that Kv10.2 KO rats demonstrated shortened onset latency, prolonged duration, and increased seizure severity when compared with wild type rats. Therefore, this study provides a new link between Kv10.2 and neuronal morphology and higher intrinsic excitability.

Detection signal amplification strategies at nanomaterial-based photoelectrochemical biosensors.

This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical (PEC) biosensors with utmost sensitivity and selectivity. These successes have partly been achieved by applying photoactive materials that significantly circumvent major limitations including poor absorption of visible light, severe aggregation of nanostructures, easy charge recombination and low conductivity. In addition, several signal enhancement techniques were also demonstrated to have effectively improved the detection performance of PEC biosensors. Accordingly, we have begun this review with a systematic introduction of the concept, working principle, and characteristics of PEC biosensors. This was followed by a discussion of a range of material modification techniques, including quantum dot modification, metal/non-metal ion doping, the formation of heterojunctions and Z-scheme composites, used in the construction of PEC biosensors. Various signal amplification strategies including quantum dot sensitisation, the application of electron donors, energy transfer effect, steric hindrances of biomolecules, and the exfoliation of biomolecules from sensing surfaces are also presented in this review. Wherever possible, we have referred to relevant examples to explain and illustrate the corresponding working mechanism and effectiveness of the nanomaterials. Therefore, this review is aimed at providing an overall view on the current trend in material modification and signal amplification strategies for the development of PEC biosensors, which will aid in stimulating ideas for future progress in this field.

Development and validation of prognosis model of mortality risk in patients with COVID-19.

This study aimed to identify clinical features for prognosing mortality risk using machine-learning methods in patients with coronavirus disease 2019 (COVID-19). A retrospective study of the inpatients with COVID-19 admitted from 15 January to 15 March 2020 in Wuhan is reported. The data of symptoms, comorbidity, demographic, vital sign, CT scans results and laboratory test results on admission were collected. Machine-learning methods (Random Forest and XGboost) were used to rank clinical features for mortality risk. Multivariate logistic regression models were applied to identify clinical features with statistical significance. The predictors of mortality were lactate dehydrogenase (LDH), C-reactive protein (CRP) and age based on 500 bootstrapped samples. A multivariate logistic regression model was formed to predict mortality 292 in-sample patients with area under the receiver operating characteristics (AUROC) of 0.9521, which was better than CURB-65 (AUROC of 0.8501) and the machine-learning-based model (AUROC of 0.4530). An out-sample data set of 13 patients was further tested to show our model (AUROC of 0.6061) was also better than CURB-65 (AUROC of 0.4608) and the machine-learning-based model (AUROC of 0.2292). LDH, CRP and age can be used to identify severe patients with COVID-19 on hospital admission.

Label-Free Imaging of Flap Endonuclease 1 in Living Cells by Assembling Original and Multifunctional Nanoprobe.

Flap endonuclease 1 (FEN1) becomes a potential tumor marker since it is closely related to cancer occurrence and development. Here, a poly dA20-mediated nanoprobe (AuNPs-poly dA20-poly dT20) was designed for FEN1 detection. Poly dA20 segment at the 3'- end of ssDNA adsorbed on AuNPs due to its strong affinity interaction with Au (stronger than Au-S bond), while the poly dT20 segment at the 5'- end overhangs. This nanoprobe not only worked as effective fluorescence quencher but also as the original nanosubstrate of FEN1. OliGreen adsorbed on poly dT20 emits strong green fluorescence because of its high sensitivity and selectivity toward thymine. However, it is quenched on the nanoprobe. In the presence of FEN1, it recognizes the overhanging poly dT20 segment and cleaves it efficiently, turning on the fluorescence of OliGreen. This indicates that the assembled nanoprobe is an effective artificial substrate to FEN1, although it is completely different from previously reported substrates that are all composed of dsDNA with a flap strand. This proposed nanoprobe was used to detect FEN1 not only in vitro but also in vivo. The method was simple, which avoided complex labeling procedures. It had a wide linear range from 0.05 U to 2 U, with the lowest detection limit of 0.007 U. Confocal imaging can distinguish cancer cells from normal cells, demonstrating its potential in clinical diagnostic and therapeutic monitoring.

Increased Expression of Kv10.2 in the Hippocampus Attenuates Valproic Acid-Induced Autism-Like Behaviors in Rats.

The role of potassium channels provides suggestive evidence for the etiology of autism. The voltage-gated potassium channel Kv10.2 (KCNH5) is widely expressed in the brain. However, the inherent relationship between Kv10.2 and autism is still unclear. Herein, a rat valproic acid (VPA)-induced autism spectrum disorder model was established. The expression level of Kv10.2 was obviously decreased in the hippocampus of VPA rats. Kv10.2 was mainly localized in neurons. Subsequently, a recombinant lentivirus expressing Kv10.2 was used to upregulate the expression of Kv10.2 in the hippocampus of VPA-exposed rats. The results were promising as injection of the Kv10.2 lentivirus in the hippocampus relieved anxiety and stereotypical behavior, and improved the social and exploratory abilities of rats that were prenatally exposed to VPA. In addition, spectral analysis of electroencephalogram data revealed that animals exposed to VPA exhibited increased high-frequency activity compared with the control rats, and this activity recovered to a certain extent after upregulation of Kv10.2 expression by lentivirus injection. These results suggest that changes in Kv10.2 may play an important role in the etiology of autism, thus providing a promising direction for further research on autism.

Amplified oxygen reduction signal at a Pt-Sn-modified TiO2 nanocomposite on an electrochemical aptasensor.

In this work, a metallic composite with strong electrocatalytic property was designed by uniformly decorating Pt and Sn nanoparticles on the surface of TiO2 nanorods (Pt-Sn@TiO2). A detection scheme was then developed based on a dual signal amplification strategy involving the Pt-Sn@TiO2 composite and exonuclease assisted target recycling. The Pt-Sn@TiO2 composite exhibited an enhanced oxygen reduction current owing to the synergistic effect between Pt and Sn, as well as high exposure of Pt (111) crystal face. Initially, a Pt-Sn@TiO2 modified glassy carbon electrode produced an amplified electrochemical signal for the reduction of dissolved oxygen in the analyte solution. Next, a DNA with a complementary sequence to a streptomycin aptamer (cDNA) was immobilised on the Pt-Sn@TiO2 modified electrode, followed by the streptomycin aptamer that hybridised with cDNA. The corresponding oxygen reduction current was diminished by 51% attributable to the hindrance from the biomolecules. After a mixture of streptomycin and RecJf exonuclease was introduced, both the streptomycin-aptamer complex and the cDNA were cleaved from the electrode, making the Pt-Sn and Pt (111) surface available for oxygen reduction. RecJf would also release streptomycin from the streptomycin-aptamer complex, allowing it to complex again with aptamers on the electrode. This has then promoted a cyclic amplification of the oxygen reduction current by 85%, which is quantitatively related to streptomycin. Under optimal conditions, the aptasensor exhibited a linear range of 0.05-1500 nM and a limit of detection of 0.02±0.0045 nM streptomycin. The sensor was then used in the real-life sample detection of streptomycin to demonstrate its potential applications to bioanalysis.

A visible light photoelectrochemical sandwich aptasensor for adenosine triphosphate based on MgIn2S4-TiO2 nanoarray heterojunction.

This work designed a MgIn2S4-TiONA heterojunction by growing MgIn2S4 nanoplates on TiO2 nanowire array (TiONA) for preparation of visible light photoelectrochemical (PEC) sensing platform. The heterojunction exhibited strong absorption of visible light, large surface area and high loading of biomolecules, leading to high sensing sensitivity. Using adenosine triphosphate (ATP), a marker of cell vitality, as the target model, a PEC sandwich aptasensor was constructed by immobilizing capture DNA1 on MgIn2S4 surface. In the presence of ATP and signal DNA2 with terminal ferrocene as the electron donor, a sandwiched DNA1-ATP-DNA2 complex could be formed on the PEC aptasensor. The aptasensor showed excellent performance with a wide linear range from 50 fM to 100 nM and a detection limit of 20 fM. The sensing performance including specificity, reproducibility, stability and practical use were also evaluated, showing promising application of the MgIn2S4-TiONA heterojunction in PEC biosensing.

A photoelectrochemical aptasensor for aflatoxin B1 detection based on an energy transfer strategy between Ce-TiO2@MoSe2 and Au nanoparticles.

In this work, a novel photoelectrochemical (PEC) aptasensor was developed for the sensitive detection of aflatoxin B1 (AFB1) based on a resonance energy transfer strategy between the Ce-TiO2@MoSe2 heterostructure and Au nanoparticles (AuNPs). The Ce-TiO2@MoSe2 composite was obtained by growing MoSe2 nanosheets on a TiO2 nanocube doped by the Ce element with a facile hydrothermal method. The composite effectively extended the absorption of TiO2 to the visible region and avoided the self-aggregation of MoSe2 nanosheets, leading to the excellent photocurrent response under visible light excitation. The PEC aptasensor was then fabricated by immobilizing the Ce-TiO2@MoSe2 composite on an ITO electrode, followed by the modification of the aminated AFB1 aptamer. An AuNP-labeled DNA sequence was subsequently hybridized with the aptamer to fabricate a sandwich structure, which was destroyed after the introduction of AFB1, decreasing the amount of the energy acceptor (AuNPs) at the electrode surface. Accordingly, the photocurrent was increased with the increase of AFB1 concentration. Under the optimal conditions, the PEC aptasensor showed a wide linear range of 0.03-200 ng mL-1 and a low detection limit of 0.01 ng mL-1 for AFB1 determination.

A highly sensitive electrochemical aptasensor for detection of microcystin-LR based on a dual signal amplification strategy.

In this work, a sensitive and selective electrochemical aptasensor for determination of microcystin-LR (MC-LR) was developed based on a dual signal amplification system consisting of a novel ternary composite and horseradish peroxidase (HRP). The ternary composite was prepared by depositing gold nanoparticles (AuNPs) on molybdenum disulfide (MoS2) covered TiO2 nanobeads (TiONBs). MoS2 nanosheet modified TiONBs provided a large surface area for immobilization of AuNPs and biomolecules. The ternary composite also possesses an improved electron transfer and catalytic capability. To construct the aptasensor, thiolated MC-LR aptamers were immobilized on the AuNP@MoS2-TiONB modified electrode through a gold-sulfur bond. Then, biotin-cDNA with a sequence complementary to the MC-LR aptamer competed with MC-LR for binding to the immobilized aptamer. The current signal catalyzed by avidin-HRP decreased with the increase of MC-LR, based on which a linear range of 0.005-30 nM and a detection limit of 0.002 nM were obtained.

Rapid detection of cocaine using aptamer-based biosensor on an evanescent wave fibre platform.

The rapid detection of cocaine has received considerable attention because of the instantaneous and adverse effects of cocaine overdose on human health. Aptamer-based biosensors for cocaine detection have been well established for research and application. However, reducing the analytic duration without deteriorating the sensitivity still remains as a challenge. Here, we proposed an aptamer-based evanescent wave fibre (EWF) biosensor to rapidly detect cocaine in a wide working range. At first, the aptamers were conjugated to complementary DNA with fluorescence tag and such conjugants were then immobilized on magnetic beads. After cocaine was introduced to compete against the aptamer-DNA conjugants, the released DNA in supernatant was detected on the EWF platform. The dynamic curves of EWF signals could be interpreted by the first-order kinetics and saturation model. The semi-log calibration curve covered a working range of 10-5000 µM of cocaine, and the limit of detection was approximately 10.5 µM. The duration of the full procedure was 990 s (16.5 min), and the detection interval was 390 s (6.5 min). The specified detection of cocaine was confirmed from four typical pharmaceutic agents. The analysis was repeated for 50 cycles without significant loss of sensitivity. Therefore, the aptamer-based EWF biosensor is a feasible solution to rapidly detect cocaine.

A glassy carbon electrode modified with a composite consisting of gold nanoparticle, reduced graphene oxide and poly(L-arginine) for simultaneous voltammetric determination of dopamine, serotonin and L-tryptophan.

A glassy carbon electrode (GCE) was modified with poly(L-arginine) (P-Arg), reduced graphene oxide (rGO) and gold nanoparticle (AuNP) to obtain an electrode for simultaneous determination of dopamine (DA), serotonin (5-HT) and L-tryptophan (L-Trp) in the presence of ascorbic acid (AA). The modified GCE was prepared via subsequent 'layer-by-layer' deposition using an electrochemical technique. The surface morphology of the modified electrode was studied by scanning electron microscopy, and electrochemical characterizations were carried out via cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode showed excellent electrocatalytic activity toward DA, 5-HT and L-Trp at pH 7.0. Figures of merit for the differential pulse voltammetric reponse are as follows: (a) Response to DA is linear in two intervals, viz. 1.0-50 nM and 1.0-50 µM DA concentration range, the typical working voltage is 202 mV (vs. Ag/AgCl), and the detection limit is 1 nM (at an S/N ratio of 3). For 5-HT, the respective data are 10 to 500 nM and 1.0 to 10 µM, 381 mV, and 30 nM. For L-Trp, the respective data are 10-70 nM and 10-100 µM, 719 mV, and 0.1 µM. The modified GCE is fairly selective. It was successfully applied to the simultaneous determination of DA, 5-HT, and L-Trp in spiked urine samples, and high recovery rates were found. Graphical abstract Schematic presentation of the voltammetric sensor based on a glassy carbon electrode modified with poly(L-arginine), reduced graphene oxide (rGO) and gold nanoparticle (GCE/P-Arg/ErGO/AuNP) for simultaneous determination of dopamine (DA), serotonin (5-HT) and L-tryptophan (L-Trp).

Ultra-sensitive electrochemical detection of oxidative stress biomarker 8-hydroxy-2'-deoxyguanosine with poly (L-arginine)/graphene wrapped Au nanoparticles modified electrode.

An innovative electrochemical sensor assembly relying on a simple "green" electrochemical reduction route is presented for the sensitive detection of 8-hydroxy-2'-deoxyguanosine (8-OHdG), the most abundant oxidative product of DNA. The sensing film consisted of poly (L-arginine) and graphene wrapped Au nanoparticles was fabricated on glassy carbon electrode (GCE/P-Arg/ErGO-AuNPs) using subsequent 'layer-by-layer' regime through electrochemical technique. The proposed method was also successfully applied for the quantification of 8-OHdG in the presence of interfering biomolecules like ascorbic acid and uric acid. Scanning electron microscopy (SEM) was utilized to characterize the surface morphology of the composite electrode. Electrochemical characterizations of the bare and modified electrodes were carried out via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). According to differential pulse voltammetry (DPV) results, there were linear relationships between the peak currents and the concentrations in the ranges of 1.0-100 nM (R2 = 0.996), and 0.5-10 µM (R2 = 0.990), with a detection limit (S/N = 3) of 1.0 nM. Furthermore, the proposed sensor was successfully applied for the determination of target analyte in human urine samples and a very high recovery percentage was obtained.