Concentration Detection Limit Research Articles

A Non‐Enzymatic and Electrochemical‐Based Sensor using a Prussian Blue‐Gold Nanoparticle‐Reduced Graphene Oxide Ternary Nanocomposite for Efficient Hydrogen Peroxide Detection.

AbstractAn electrochemical sensor has been developed using PBNCs/AuNPs/RGO ternary nanocomposite, in which gold nanoparticles (AuNPs) are deposited on Prussian blue nanocubes (PBNCs) and reduced graphene oxide (RGO) using two‐step in‐situ synthetic approach. The synthesized ternary nanocomposite shows high catalytic activity towards H2O2 sensing due to the synergistic effect of gold nanoparticles and RGO. The material was prepared by the co‐precipitation method, and the morphology of the synthesized composites was characterized using X‐Ray diffraction (XRD), scanning electron microscopy (SEM), and High‐resolution Transmission electron microscopy (HR‐TEM). Electrochemical measurements were performed by modifying glassy carbon electrodes (GCE) with bare PBNCs, PBNCs/RGO, and PBNCs/AuNPs/RGO for low‐level detection of H2O2 using Cyclic Voltammetry (CV) and Chronoamperometry. The interference property was analyzed using ascorbic acid (AA), uric acid (UA), and glucose as interfering agents. The modified electrode shows high sensitivity of 5.47 nA/nM and a limit of detection of 260 pM for H2O2 at (S/N=3). This electrochemical sensor observed a linear range of detection from 0.66 nM to 10.53 nM. The proposed sensor exhibits good stability, better selectivity, and a picomolar concentration detection limit for H2O2.

Determination of oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine products in human very low-density lipoproteins by nonaqueous low-flow capillary electrophoresis-mass spectrometry

A simple and fast low-flow capillary electrophoresis-mass spectrometry (low-flow CE-MS) method has been developed to analyze oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (ox-PAPC) products in human very low-density lipoproteins (VLDLs). Native PAPC standard was analyzed to optimize the low-flow CE-MS method. The optimal CE conditions included separation buffer (60% (v/v) acetonitrile, 40% (v/v) methanol, 0.1% (v/v) water, 0.5% (v/v) formic acid, 20 mM ammonium acetate), sheath liquid (60% (v/v) acetonitrile, 40% (v/v) methanol, 0.1% (v/v) water, 20 mM ammonium acetate), separation voltage (20 kV), separation capillary internal diameter (i.d.) (75 µm), separation capillary temperature (23˚C) and sample injection time (6 s). The selected MS conditions included heated capillary temperature (250°C), capillary voltage (10 V), and injection time (1 s). Sheath gas was not used in this study. The total ion chromatograms (TICs), extracted ion chromatograms (EICs) and MS spectra of native PAPC standard and its in vitro oxidation products showed good repeatability and sensitivity. To determine the ox-PAPC products in human VLDLs, the EICs and MS spectra of VLDLs were compared with the in vitro oxidation products of native PAPC standard. For native PAPC standard, the measured linear range was 2.5 - 100.0 µg/mL, and the coefficients of determination (R2) was 0.9994. The concentration limit of detection (LOD) was 0.44 µg/mL, and the concentration limit of quantitation (LOQ) was 1.34 µg/mL. A total of 21 ox-PAPC products were analyzed for the VLDLs of healthy and uremic subjects. The levels of 7 short-chain and 5 long-chain ox-PAPC products on uremic VLDLs were significantly higher than healthy VLDLs. This simple low-flow CE-MS method might be a good alternative for LC-MS for the analysis of ox-PAPC products. Furthermore, it might also help scientists to expedite the search for uremic biomarkers.

Removal of Cd (II) Ions from Water Solutions Using Dispersive Solid-Phase Extraction Method with 2-aminopyridine/graphene Oxide Nano-Plates

Background: The effluent release containing heavy metals as Cd (II) ions has drastic risks to both the natural environment and human health. In this research, a novel nano sorbent from the pyridine derivative was prepared for dispersive solid-phase extraction of Cd (II) ions. Methods: Graphene oxide (GrO) was chemically modified by a 2-aminopyridine group (2Ap) through a multistep procedure. The affection of adsorbent amount, pH, temperature, equilibrium time on its sorption with Gr2Ap adsorbent was studied and Gr2Ap adsorbent displayed a high ability to adsorb Cd (II) at pH=6. Furthermore, to inquire about the adsorption isotherms of metal ions sorption mechanism, the model of Freundlich and Langmuir was fitted to empirical isotherm data. Besides, to inspect the basic process of the metal sorption mechanism pseudo-first and second-order kinetic, and Roginsky-Zeldovich types were compatible with adsorption kinetic results. Results: The concentration factor and limit of detection for Cd (II) were 12.5 and 1.84 µg/L, respectively. According to the value of the correlation coefficient factor, that the Gr2Ap adsorbent exhibits the highest ability to adsorb Cd (II) ions (22.54 mg/g) at pH=6. The pseudo-second-order pattern of Cd (II) adsorption fits best with the kinetic result. Conclusion: The Gr2Ap exhibited a high potential for removing the heavy metal ions from aqueous samples. Besides, the current research was shown an efficient, easy, inexpensive, and selectable method for evaluating the Cd (II) ions in several samples of water and wastewater.

Hypertension as One of the Main Non-Myocardial Infarction-Related Causes of Increased Cardiospecific Troponins: From Mechanisms to Significance in Current Medical Practice.

It is well known that many pathological conditions of both cardiovascular diseases (CVDs) (coronary heart disease, myocardial infarction, arrhythmias, myocarditis, cardiomyopathy, etc.) and non-cardiac (sepsis, anemia, kidney diseases, diabetes mellitus, etc.) origin in the course of their development cause injury to contractile cardiac muscle cells - myocardial cells (MCs). One of the most sensitive and specific criteria for detecting MC injury are cardiospecific troponins (CTs), which are regulatory protein molecules that are released into the blood serum from MC upon their death or injury. Current methods for determining CTs are called high-sensitive ones, and their main advantage is a very low minimum detectable concentration (limit of detection) (average 1 - 10 ng/L or less), which allows early detection of minor MC injury at the earliest stages of CVDs, and therefore they can change the understanding of disease development mechanisms and open up new diagnostic possibilities. One of the most common and dangerous early diseases of the cardiovascular system is hypertension (HT). The novelty of this article lies in the discussion of a new diagnostic direction - predicting the risk of developing CVDs and their dangerous complications in patients with HT by determining the concentration of CTs. In addition, pathophysiological mechanisms underlying MC injury and the release of CTs into the bloodstream and the elimination of CTs into the urine are proposed. This information will contribute to additional fundamental and clinical research to verify the new diagnostic possibility of using CTs in clinical practice (for the management of patients with HT).

Polydopamine imprinted polymer-based tunable electrochemical synthesis of copper benzene-1, 3, 5-tricarboxylate metal-organic framework film as a hybrid dual recognition element for ultra-trace sensing of pregabalin (lyrica)

The present study propounds an innovative diagnostic hybrid dual recognition strategy to detect trace amounts of pregabalin (PGB) using the combination of two powerful metal-organic framework (MOF) structures and the molecularly imprinted polymer (MIP) technique. To improve the analytical property of the electrode surface, copper-benzene-1,3,5-tricarboxylic acid frameworks (Cu-BTC MOFs) were directly synthesized on the glassy carbon electrode (GCE). Afterwards, MIP film was synthesized via the in situ dopamine (DA) electropolymerization method. To explore the effect of independent variables on the MIP construction, the Box-Behnken design was considered to determine the response surface methodology. In this sense, the predicted optimum combination variables were DA= 3 mM, pH = 7.4, cycle number = 16, KOH 4 mM, KOH: Et-OH ratio of 5:1 and 18 min elution time. Incubation time was obtained at 12 min. Electrochemical impedance spectroscopy (EIS) was used to determine the PGB analyte. The linear dynamic concentration range and limit of detection (LOD) were 0.05–800 pM and 2.9 fM, respectively. The imprinting calculated factor was 24.60, showing high interaction between the PGB and DA monomer. Inter-day and intra-day reproducibility measurements showed 2.08% and 1.58% and, 98% of the initial current response was maintained. Coefficients of selectivity against the PGB, for tapentadol, gabapentin, levetiracetam, L -Carnitine, and L -Histidine were 1, 5.52, 8.75, 2.8, 6.56 and 6.56 respectively. Cyclic voltammetry (CV) at various scan rates verified that adsorption kinetics follows a diffusion control mechanism. Finally, the efficiency of the GCE/Cu-BTC/ePDA-MIP sensor in real samples was evaluated and satisfactory results were achieved. • Combining two powerful molecularly imprinted polymer and metal-organic framework methods. • Direct growth of copper-organic framework mediated by copper hydroxide nano-strips. • In situ dopamine potentiodynamic electropolymerization. • Optimize electropolymerization conditions with Box-Behnken method. • Ultra-trace detection of pregabalin by prepared sensor.

Sensitive Label‐Free Immunoassay by Colorimetric Plasmonic Biosensors Using Silver Nanodome Arrays

The sensitive direct detection of biomolecules is demonstrated by a colorimetric plasmonic biosensor utilizing the surface colors of plasmonic metasurfaces named Ag nanodome arrays. The Ag nanodome arrays consist of polystyrene bead monolayers coated with Ag thin films whose surface colors are optimized by changing the size of the polystyrene beads. The bulk refractive index sensitivity of colorimetric detection evaluated using the hue angle is 590° RIU−1 (RIU: refractive index unit). For selected geometry, the refractive index resolution (5.0 × 10−5 RIU) obtained by colorimetric detection surpasses that of spectroscopic detection evaluated via the dip wavelength in the reflection spectrum. The numerical simulations predict an enhanced sensing performance when the hue angle of the surface colors of the Ag nanodome arrays changes from 300° to 200°, corresponding to changes in the dip wavelength from 570 to 600 nm in the reflection spectra. Furthermore, the detection sensitivity of the biomolecules is characterized using a direct IgG immunoassay format. The detection limit of the IgG concentration is as low as 134 pM using simple colorimetric detection. The feasibility of sensitive label‐free immunoassays using a colorimetric plasmonic biosensor is expected to accelerate the development of highly sensitive and reliable smartphone‐based plasmonic biosensors.

A bottom-up sonication-assisted synthesis of Zn-BTC MOF nanosheets and the ppb-level acetone detection of their derived ZnO nanosheets

Two-dimensional metal-organic framework nanosheets, as a new member of the two-dimensional family, are attracting increasing research interest in various fields. Herein, a uniform two-dimensional Zn-BTC MOF nanosheet with a thickness of 14 ± 2 nm was synthesized through a simple, efficient, and scalable sonication-assisted bottom-up strategy. The ZnO nanoparticles were used as the Zn source, which can be corroded by H3BTC to form Zn-BTC MOFs under sonication conditions. The morphologies of Zn-BTC MOFs can be modulated from nanosheets to nanorods by changing the content of H3BTC. The crystal growth process is dominated by the thermodynamics of sonication and the stoichiometric ratio of the generated Zn2+ and H3BTC, and the crystal growth mechanism was elaborated by the oriented attachment. Consequently, a chemiresistive gas sensor based on Zn-BTC nanosheet derivatives was fabricated to detect ppb-level acetone. Notably, the experimental detection limit of concentration could reach as low as 100 ppb of acetone due to the functional surface, and the dynamic response linearity reached 99 %. Our work explored a new method of synthesizing two-dimensional Zn-BTC MOF, and the fabricated gas sensing device demonstrated promising potential in gas sensing fields.

Hybrid Carbon Nanotubes/Gold Nanoparticles Composites for Trace Nitric Oxide Detection over a Wide Range of Humidity

Composites of functionalized single walled carbon nanotubes (SWCNTs) and gold nanoparticles (Au NPs) of ≈15 nm diameter were drop-cast on a printed circuit board (PCB) substrate equipped with interdigitated electrodes to make a hybrid thin film. Addition of Au NPs decorated the surface of SWCNTs networked films and acted as catalysts which resulted into an enhanced sensitivity and low ppb concentration detection limit. The compositions of the film were characterized by scanning electron microscope (SEM). SWCNTs clusters were loaded with various amount of Au NPs ranging from 1–10% (by weight) and their effect on Nitric oxide (NO) sensitivity was studied and optimized. Further, the optimized composite films were tested in both air and nitrogen environments and as well as over a wide relative humidity range (0–97%). Sensors were also tested for the selectivity by exposing to various gases such as nitrous oxide, ammonia, carbon monoxide, sulfur dioxide and acetone. Sensitivity to NO was found much higher than the other tested gases. The advantage of this sensor is that it is sensitive to NO at low ppb level (10 ppb) with estimated response time within 10 s and recovery time around 1 min, and has excellent reproducibility from sensor to sensor and works within the wide range of relative humidity (0–97%).

Ingenious Fabrication of Ag-Filled Porous Anodic Alumina Films as Powerful SERS Substrates for Efficient Detection of Biological and Organic Molecules.

Surface-enhanced Raman scattering (SERS) has been widely used to effectively detect various biological and organic molecules. This detection method needs analytes adsorbed onto a specific metal nanostructure, e.g., Ag-nanoparticles. A substrate containing such a structure (called SERS substrate) is user-friendly for people implementing the adsorption and subsequent SERS detection. Here, we report on powerful SERS substrates based on efficient fabrication of Ag-filled anodic aluminum oxide (AAO) films. The films contain many nanopores with small as-grown inter-pore gap of 15 nm. The substrates are created by electrochemically depositing silver into nanopores without an additional pore widening process, which is usually needed for conventional two-step AAO fabrication. The created substrates contain well-separated Ag-nanoparticles with quite a small inter-particle gap and a high number density (2.5 × 1010 cm−2). We use one-step anodization together with omitting additional pore widening to improve the throughput of substrate fabrication. Such substrates provide a low concentration detection limit of 10−11 M and high SERS enhancement factor of 1 × 106 for rhodamine 6G (R6G). The effective detection of biological and organic molecules by the substrate is demonstrated with analytes of adenine, glucose, R6G, eosin Y, and methylene blue. These results allow us to take one step further toward the successful commercialization of AAO-based SERS substrates.

Synthesis of the polymers containing norbornene and tetraphenylethene by ring-opening metathesis polymerization and their structural characterization, aggregation-induced emission and aniline detection

Well-defined norbornene-based homopolymers and block copolymers containing tetraphenylethene or fluorinated tetraphenylethene moieties were synthesized by ring-opening metathesis polymerization of the corresponding monomers using the third-generation Grubbs' initiator. The molecular weight of the polymers is close to the theoretical molecular weight and the polydispersity index is as low as 1.01 to 1.07. All polymers exhibit aggregation-induced emission characteristics and reveal high emission in solid state and aggregate state. In general, the quantum yield of the polymers in aggregate state is more than 100 times higher than that of the solution. The sensing ability of the polymers for aniline in the aggregated state exhibits the detection limit of concentration of 5 × 10−6 M. In addition, the minimum concentration of aniline detected by fluorescent test papers is as low as 10−3 to10−4 M.

Development and application of a multiplex PCR method to differentiate Salmonella enterica serovar Typhimurium from its monophasic variants in pig farms

Salmonella enterica serovar Typhimurium monophasic variants (Salmonella 4,[5],12:i:-) has increased dramatically, causing human salmonellosis and colonization in pigs. With a difference to S. Typhimurium, the monophasic variants of S. Typhimurium lose the gene cassettes encoding the second phase flagellin. To establish a rapid method to detect and differentiate the two serotypes, we analyzed the published 679 genomes of S. Typhimurium and its monophasic variants and found that no Salmonella 4,[5],12:i:- strains carry both fljB and hin genes. Therefore, we established a novel multiplex PCR method using the fljB-hin region and mdh gene as target sequences to detect and differentiate both serotypes. This method can be used to specifically detect both serotypes with a detection limit for DNA concentration at 10 pg/μL. In addition, the PCR assay successfully differentiated 36 S. Typhimurium isolates from 62 isolates of monophasic variants preserved in our laboratory from 2009 to 2017, which corresponds to the whole-genome-based serotyping results. Application of the multiplex PCR method to 60 fecal samples from a pig farm identified 11.7% (7/60) of S. Typhimurium monophasic variants, which is consistent with the whole-genome-based serotyping results. The multiplex PCR assay is a rapid and precise method for the detection of S. Typhimurium monophasic variants from samples across food production chains.

Terahertz Plasmonic Sensor Based on Metal-Insulator Composite Woven-Wire Mesh.

Terahertz (THz) spectroscopy has been proven as an effective detection means for the label-free and nondestructive sensing of biochemical molecules based on their unique roto-vibrational transitions. However, the conventional THz spectroscopic system is unsuitable for minute material sensing due to its far-field detection scheme, low sample amount, and lack of spectral characteristics, leading to low absorption cross-sections and sensitivity. In this study, a 3D plasmonic structure based on a metal-coated woven-wire mesh (MCWM) was experimentally and numerically demonstrated for sensing trace amounts of analytes combined with THz spectroscopy. Dual sharp spectral features were exhibited in the transmission spectrum, originating from the resonant excitation of THz surface electromagnetic modes via the aperture and periodicity of the MCWM unit cell. According to the finite element simulation, an enhanced and localized surface field was formed at THz resonant frequencies and was concentrated at the metal gaps near the periodic corrugations of the MCWM, resulting in enormous resonant dip shifts caused by the tiny variations in membrane thicknesses and refractive indices. Different types and quantities of analytes, including hydrophilic biopolymer (PAA) membrane, nonuniformly distributed microparticles to mimic macro-biomolecules or cells, and electrolyte salts of PBS, were successfully identified by the MCWM sensor with the best thickness and refractive index sensitivities approaching 8.26 GHz/μm and 547 GHz/RIU, respectively. The demonstrated detection limit of thickness and molecular concentration could respectively achieve nanometer and femtomolar scales in PAA macromolecular detection, surpassing the available metallic mesh devices. The MCWM-based sensing platform presents a rapid, inexpensive, and simple analysis method, potentially paving the way for a new generation of label-free microanalysis sensors.

Analysis of Oxidized 1-Palmitoyl-2-Arachidonoyl-Sn-Glycero-3 Phosphocholine Products in Uremic Patients by LC-ESI/MS

A simple liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI/MS) method has been developed to analyze oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (ox-PAPC) products on the lipoproteins of uremic patients. The native PAPC standard was in vitro oxidized by the Fenton reaction, and the ox-PAPC products were analyzed by LC- ESI/MS. For LC, a C8 column and a mobile phase (acetonitrile-isopropanol containing 0.1% formic acid (70:30, v/v)) were selected. For ESI/MS, the optimal conditions included sheath gas pressure (10 psi), capillary temperature (270 °C), and injection time (1000 ms). The identification of ox-PAPC products on human lipoproteins was based on the extracted ion chromatograms (EICs) and the ESI-MS spectra of the in vitro oxidation products of PAPC standard. The EICs and ESI-MS spectra showed good repeatability and sensitivity. A total of 21 ox-PAPC products was determined. Linear analysis has been performed for the phospholipid standard, 1, 2-Di-O-hexadecyl-sn-glycero-3-phosphocholine (PC(O-16:0/O-16:0)). The linear range was 5.0–100.0 µg/mL, and the coefficient of determination (R2) was 0.989. The concentration limit of detection (LOD) was 1.50 µg/mL, and the concentration limit of quantitation (LOQ) was 4.54 µg/mL. The selected 21 ox-PAPC products have been identified and quantified in very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) of uremic and healthy subjects. Interestingly, the results showed that the levels of 18 products in VLDL, one product in LDL, and 19 products in HDL were significantly higher for uremic patients than healthy controls. This simple LC-ESI/MS method might accelerate the searching for biomarkers of uremia in the future.

Signal-On and Highly Sensitive Electrochemiluminescence Biosensor for Hydrogen Sulfide in Joint Fluid Based on Silver-Ion-Mediated Base Pairs and Hybridization Chain Reaction

Hydrogen sulfide (H2S) in joint fluid acts as a signal molecule to regulate joint inflammation. Direct detection of H2S in joint fluid is of great significance for the diagnosis and treatment of arthritis. However, due to the low volume of joint fluid and low H2S concentration, existing methods face the problem of the insufficient limit of detection. In this study, a highly sensitive biosensor was proposed by designing a primer probe and combining it with hybrid chain reaction (HCR) under the strong interaction between metal ions and H2S to achieve H2S detection. The primer probe containing multiple cytosine (C) sequences was fixed on a gold electrode, and the C–Ag–C hairpin structure was formed under the action of Ag+. In the presence of H2S, it can combine with Ag+ in the hairpin structure to form Ag2S, which leads to the opening of the hairpin structure and triggers the hybridization chain reaction (HCR) with another two hairpin structures (H1 and H2). A large number of double-stranded nucleic acid structures can be obtained on the electrode surface. Finally, Ru(phen)32+ can be embedded into the double chain structure to generate the electrochemiluminescence (ECL) signal. The linear response of the H2S biosensor ranged from 0.1000 to 1500 nM, and the limit of detection concentration of H2S was 0.0398 nM. The developed biosensor was successfully used to determine H2S in joint fluid.

Tuning the sensing responses towards room-temperature hypersensitive methanol gas sensor using exfoliated graphene-enhanced ZnO quantum dot nanostructures

A suitable and non-invasive methanol sensor workable in ambient temperature conditions with a high response has gained wide interest to prevent detrimental consequences for industrial workers from its low-level intoxication. In this work, we present a tunable and highly responsive ppb-level methanol gas sensor device working at room temperature via a bottom-up synthetic approach using exfoliated graphene sheet (EGs) and ZnO quantum dots (QDs) on an aluminum anodic oxide (AAO) template. It is verified that EGs-supported AAO with a vertical electrode configuration enabled high and fast-responsive methanol sensing. Moreover, the hydroxyl and carboxyl groups of the high surface area EGs and ZnO QDs with a 3.37 eV bandgap efficiently absorbing UV light led to 56 times high response due to the enhanced polarization on the sensor surface compared to non-UV-radiated EGs/AAO at 800 ppb of methanol. The optimal resonance frequency of methanol is determined to be 100 kHz, which could detect methanol with high response of 2.65% at 100 ppm. The limit of detection (LOD) concentration is obtained at 2 ppb level. This study demonstrates the potential of UV-assisted ZnO, EGs, and AAO-based capacitance sensor material for rapidly detecting hazardous gaseous light organic molecules at ambient conditions, and the overall approach can be easily expanded to a novel non-invasive monitoring strategy for light and hazardous volatile organic exposures.

Recent Developments for the Detection of Escherichia Coli Biosensors Based on Nano-Objects—A Review

Advances in nanotechnology have made it possible in recent years to develop strategies for rapid and sensitive detection of pathogenic bacteria using new nanomaterials and the development of electronic nano-sensors. The detection of bacteria still faces problems such as long analysis time and complexity of the process. An alternative method is the use of biosensors, which combines a biological recognition mechanism with a physical transduction technique. Thus, a number of methods and manufacturing technologies have been developed in order to achieve performance in sensitivity, detection limit, label-free detection or real-time analysis. This review aims to focus on the state of the art of biosensors for the recognition elements of Escherichia coli in label-free biosensors with a particular focus on the beneficial use of nanomaterials and nano-objects for detection. Among the recent related biosensors based on nano-objects for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E. coli</i> detection, the technologies and measurement techniques are detailed by comparing their performances detection in terms of concentration range and detection limit. Detection becomes more sensitive and more flexible using nanoparticles as markers, and real-time electrical detection methods are dominant in comparison with optical ones. The lowest detection limit can be achieved for sensors based on metal (gold or silver nanoparticles) with optical detection techniques in contrast with electrical detection methods using measurement conductance.

Laser-induced breakdown spectroscopy signal enhancement effect for argon caused by the presence of gold nanoparticles

The effect of the presence of nanoparticles (NPs) on the laser induced breakdown spectroscopy (LIBS) signal of argon gas was studied experimentally. 10–20 nm diameter gold NPs, produced by a spark discharge nanoparticle generator, were suspended in argon gas. The effect of particle size, number concentration and mass concentration, as well as laser pulse energy on the LIBS argon signal was systematically investigated. It was found that the breakdown threshold of the gas decreases considerably, facilitating the detection of Ar emission at such laser fluences, which do not allow plasma formation without the presence of the NPs. Our observations persist even at aerosol mass concentrations that are too low to allow the direct detection of nanoparticles. The effect, which is attributed to electron thermo- and field emission induced by the high intensity laser pulse, shows an asymptotically increasing magnitude with the aerosol mass concentration. The signal enhancement was found to be 102–104 and the effect is suggested to be useful in trace gas analysis or for the indirect detection of NPs. The achievable indirect aerosol mass concentration detection limit was estimated to be in the parts per trillion regime (as low as 50 ng·m−3), which is comparable to the best literature values reported for direct analysis.

Wafer‐Scale 2H‐MoS2 Monolayer for High Surface‐enhanced Raman Scattering Performance: Charge‐Transfer Coupled with Molecule Resonance

AbstractThe surface‐enhanced Raman scattering (SERS) as a novel and efficient analytic technique to probe molecules has attracted tremendous attention. Semiconducting substrates have been widely investigated for their applications into SERS because of their easy integration with electronic devices. In this work, a wafer‐scale semiconducting MoS2 monolayer (2H‐MoS2‐ML) without additional treatment is used as the SERS substrate, which shows the naturally formed MoS2 ML has excellent chemical stability, high uniformity, and high sensitivity. It is found that the detection concentration limit can reach 1 × 10−8 m and the enhancement factor is about 4.5 × 106 for the rhodamine 6G (R6G) under a 532 nm excitation laser, which is the highest SERS performance observed on 2H‐MoS2‐ML up to now. The experimental and computational studies reveal that the photo‐enhanced charge transfer coupled with molecule resonance contribute to remarkable SERS. In addition to R6G, 2H‐MoS2‐ML shows good SERS signals on the detection of amaranth and crystal violet too. The findings not only provide an insightful understanding of the mechanism for the improved SERS performance of semiconducting transition‐metal dichalcogenides (TMDs) MLs, but are helpful for the design of novel SERS substrates. It is expected that the wafer‐scale TMDs may find practical applications in SERS.

Development of a noncompetitive magnetic-phage anti-immunocomplex assay for detecting of organophosphorus pesticides with a thiophosphate group

Organophosphorus pesticides (OPs) are widely used in agriculture and the monitoring of their residues is very important to protect human health. Immunoassays are important tools for the analysis of small molecules. Generally, noncompetitive mode of immunoassay is considered to be more sensitive than competitive mode. In this study, peptides that can identify immunocomplex of OPs were screened from a phage display library. Subsequently, a second-generation peptide library was constructed and peptides with better performance were isolated. Then, a rapid and sensitive noncompetitive magnetic-phage anti-immunocomplex assay (MPHAIA) for OPs was developed based on the best phage-peptide and single chain antibody immunomagnetic beads. The MPHAIA showed broad specificity for OPs with a thiophosphate group. The half-saturated concentration (SC50) values and limits of detection (LODs) of MPHAIA to 12 OPs were ranged from 15.04 to 105.48 ng/mL and 4.07–14.19 ng/mL, respectively. The accuracy and reliability of MPHAIA were verified by gas chromatography-tandem mass spectrometry (GC-MS/MS) parallel analysis of six kinds of OPs in spiked cucumber samples. The recovery rates were in range of 81.2–116.3% with coefficient of variation from 4.1% to 14.1%, which were consistent with the results of GC-MS/MS.

Combining 2D organic and 1D inorganic nanoblocks to develop free-standing hybrid nanomembranes for conformable biosensors

We report a simple approach to fabricate free-standing perforated 2D nanomembranes hosting well-ordered 1D metallic nanostructures to obtain hybrid materials with nanostructured surfaces for flexible electronics. Nanomembranes are formed by alternatively depositing perforated poly(lactic acid) (PLA) and poly(3,4-ethylenedioxythiophene) layers. Copper metallic nanowires (NWs) were incorporated into the nanoperforations of the top PLA layer by electrodeposition and further coated with silver via a transmetallation reaction. The combination of 2D polymeric nanomembranes and aligned 1D metallic NWs allows merging the flexibility and conformability of the ultrathin soft polymeric nanomembranes with the good electrical properties of metals for biointegrated electronic devices. Thus, we were able to tailor the nanomembrane surface chemistry as it was corroborated by SEM, EDX, XPS, CV, EIS and contact angle. The obtained hybrid nanomembranes were flexible and conformable showing sensing capacity towards H2O2 with good linear concentration range (0.35–10 mM), sensitivity (120 µA cm−2 mM−1) and limit of detection (7 μm). Moreover, the membranes showed good stability, reproducibility and selectivity towards H2O2.