Concentration Detection Limit Research Articles

Hierarchically In2S3@In2O3 Nanorods Heterojunctions for Enhanced NO2 Sensing at Lower Operating Temperature

Hierarchically structured In2S3@In2O3 nanorods were synthesized via a two-step hydrothermal method. Compared to single-component In2O3 based sensors, the as-developed In2S3@In2O3 nanorods based chemiresistive-type sensor exhibited significantly enhanced response and reduced operating temperature. The sensor displayed a response of approximately 51.2 to 3 ppm NO2 at 120℃, with a response time and recovery time of 76 and 48seconds, respectively, and a detection limit of NO2 concentration to 0.014 ppm. By constructing In2S3@In2O3 heterojunctions, the optimal operating temperature has been effectively lowered from 160℃ to 120℃. The improved sensing performance is attributable to the nano-heterojunctions formed between In2S3 and In2O3, which increase the specific surface area to provide additional active adsorption sites, and as well, prevent the shielding effect of surface-adsorbed oxygen on NO2. Density functional theory (DFT) calculations demonstrated that the introduction of heterojunctions of In2S3@In2O3 enhances the adsorption energy and charge transfer between NO2 and the sensing material.

Proposed Detection Limits for Radioactivity Concentrations in Water in the Decommissioning and Dismantling of Nuclear Facilities

The Dismantling and Decommissioning (D&D) of nuclear facilities poses several challenges for radioactivity measurement laboratories involved in environmental radiation monitoring plans. One of them is the definition of the detection limits to be achieved for the radionuclides analysis in different samples. The detection limits should be set in such a way that the obtained concentration values for each radionuclide are easily discriminated from certain maximum activity concentration levels. These maximum activity concentration levels are usually set in view of the respective dose contributions from each radionuclide. There are some national legislations that settle detection limits for drinking water. However, there is no regulation containing detection limits for groundwater or surface water. In this way, different institutions or companies require very different detection limits for radioactivity concentration assessment in those types of water associated with D&D activities. In this work, we focus on the detection limits required for the D&D activities in rainwater, surface water and groundwater. We propose detection limits obtained by applying the WHO methodology for maximum activity concentration levels and compare with those requested by radioactive waste management agencies and regulatory bodies. Some real cases where our proposal allows identification of events are analysed and conclusions are extracted.

Paper-based radial chromatographic assay for rapid in situ measurement of gelatinized starch concentration

Starch gelatinization is pivotal in food processing, impacting viscosity, texture, and functionality. However, current methods for determining concentration and viscosity of gelatinized starch (GS), such as falling ball and rotational viscometers, are impractical for in situ measurements due to bulky equipment. Here, we introduce a paper-based radial chromatographic assay (PRCA) method for rapidly measuring the concentration of gelatinized starch (GS). We utilized Evans Blue (EB) as a chromatic agent to label GS and generate color-ring patterns on a nitrocellulose membrane based on the “Coffee-ring” effect. The resulting PRCA patterns varied depending on the GS concentrations, yielding a good linear correlation (R2 > 0.967) between grayscale value and viscosity. This method enables rapid measurement of GS concentration within 10 s, even with varying ratios of amylose to amylopectin. PRCA demonstrates a detection limit for GS concentration between 0.027% and 0.051%, which is 10-20 fold lower than that of traditional rotational-viscometer. The intensity of PRCA patterns at pH 3 (45.8) was significantly lower than those at higher pH levels (5 to 9), consistent with the decreased viscosity measured by the viscosimeter. The intensity of PRCA patterns did not change with increasing temperature from 25°C to 90°C, despite the significant decrease in viscosity from 345 mPa•s to 195 mPa•s. Additionally, PRCA can monitor changes in starch viscosity during the hydrolysis process, which decreases from 744 mPa•s to 6 mPa•s. This capability provides an efficient means of measuring the concentration and viscosity of GS during food processing.

Fluorescence Sensing of Eclampsia Biomarkers via the Immunosorbent Atom Transfer Radical Polymerization Assay.

Accurate and quantitative detection of pre-eclampsia markers is crucial in reducing pregnancy mortality rates. This study introduces a novel approach utilizing a fluorescent biosensor by the immunosorbent atom transfer radical polymerization (immuno-ATRP) assay to detect the pre-eclampsia protein marker CD81. The critical step used in this sensor is the novel signal amplification strategy of fluorescein polymerization mediated by ferritin-enhanced controlled radical polymerization, which combines with a traditional enzyme-linked immunosorbent assay (ELISA) to further reduce the detection limit of the CD81 protein concentration. The fluorescence intensity was linear versus logarithmic CD81 protein concentration from 0.1 to 10,000 pg mL-1, and the detection limit was 0.067 pg mL-1. Surprisingly, in 30% normal human serum (NHS), the sensor can also detect target protein over 0.1-10,000 pg mL-1, with 0.083 pg mL-1 for the detection limit. Moreover, the proposed biosensor is designed to be cost-effective, making it accessible, particularly in resource-limited settings where expensive detection techniques may not be available. The affordability of this method enables widespread screening and monitoring of preeclampsia, ultimately benefiting many pregnant women by improving their healthcare outcomes. In short, developing of a low-cost and susceptible direct detection method for preeclampsia protein markers, such as CD81, through the use of the immuno-ATRP assay, has significant implications for reducing pregnancy mortality. This method holds promise for early detection, precise treatment, and improved management of preeclampsia, thereby contributing to better maternal and fetal health.

Advancing Simultaneous Extraction and Sequential Single-Particle ICP-MS Analysis for Metallic Nanoparticle Mixtures in Plant Tissues.

Engineered nanoparticles (ENPs) have been increasingly used in agricultural operations, leading to an urgent need for robust methods to analyze co-occurring ENPs in plant tissues. In response, this study advanced the simultaneous extraction of coexisting silver, cerium oxide, and copper oxide ENPs in lettuce shoots and roots using macerozyme R-10 and analyzed them by single-particle inductively coupled plasma-mass spectrometry (ICP-MS). Additionally, the standard stock suspensions of the ENPs were stabilized with citrate, and the long-term stability (up to 5 months) was examined for the first time. The method performance results displayed satisfactory accuracies and precisions and achieved low particle concentration and particle size detection limits. Significantly, the oven drying process was proved not to impact the properties of the ENPs; therefore, oven-dried lettuce tissues were used in this study, which markedly expanded the applicability of this method. This robust methodology provides a timely approach to characterize and quantify multiple coexisting ENPs in plants.

Development and application of a TaqMan-probe-based multiplex real-time PCR assay for simultaneous detection of porcine circovirus 2, 3, and 4 in Guangdong province of China.

Porcine circoviruses disease (PCVD), caused by porcine circovirus (PCVs), is an important swine disease characterized by porcine dermatitis, nephrotic syndrome and reproductive disorders in sows. However, diseases caused by PCV2, PCV3, or PCV4 are difficult to distinguish, so a simple, rapid, accurate and high-throughput diagnostic and identification method is urgently needed to differentiate these three types. In this study, specific primers and probes were designed based on the conserved region sequences of the Rep gene of PCV2, and the Cap gene of PCV3 and PCV4. A multiplex qPCR assay was developed and optimized that the limit of detection concentration could reach as low as 3.8 copies/μL, with all correlation coefficients (R2) exceeding 0.999. Furthermore, the method showed no cross-reaction with other crucial porcine viral pathogens, and both intra-repeatability and inter-reproducibility coefficients of variation were below 2%. The assay was applied to the detection of 738 pig samples collected from 2020 to 2021 in Guangdong Province, China. This revealed positive infection rates of 65.18% for PCV2, 29.27% for PCV3, and 0% for PCV4, with a PCV2/PCV3 co-infection rate of 23.17%. Subsequently, complete genome sequences of 17 PCV2 and 4 PCV3 strains were obtained from the above positive samples and pre-preserved positive circovirus samples. Nucleotide sequence analysis revealed that the 17 PCV2 strains shared 96.7-100% complete nucleotide identity, with 6 strains being PCV2b and 11 strains being PCV2d; the 4 PCV3 strains shared 98.9-99.4% complete nucleotide identity, with 2 strains being PCV3a-1 and 2 strains being PCV3b. This research provides a reliable tool for rapid PCVs identification and detection. Molecular epidemiological investigation of PCVs in pigs in Guangdong Province will help us to understand PCV2 and PCV3 epidemiological characteristics and evolutionary trends.

Nitroxyl donating and visualization with a coumarin-based fluorescence probe

Nitroxyl (HNO), the single-electron reduction product of nitric oxide (NO), has attracted great interest in the treatment of congestive heart failure in clinical trials. In this paper, we describe the first coumarin-based compound N-hydroxy-2-oxo-2H-chromene-6-sulfonamide (CD1) as a dualfunctional HNO donor, which can release both an HNO signaling molecule and a fluorescent reporter. Under physiological conditions (pH 7.4 and 37 °C), the CD1 HNO donor can readily decompose with a half-life of ∼90 min. The corresponding stoichiometry HNO from the CD1 donor was confirmed using both Vitamin B12 and phosphine compound traps. In addition to HNO releasing, specifically, the degradation product 2-oxo-2H-chromene-6-sulfinate (CS1) was generated as a fluorescent marker during the decomposition. Therefore, the HNO amount released in situ can be accurately monitored through fluorescence generation. As compared to the CD1 donor, the fluorescence intensity increased by about 4.9-fold. The concentration limit of detection of HNO releasing was determined to be ∼0.13 μM according to the fluorescence generation of CS1 at physiological conditions. Moreover, the bioimaging of the CD1 donor was demonstrated in the cell culture of HeLa cells, where the intracellular fluorescence signals were observed, inferring the site of HNO release. Finally, we anticipate that this novel coumarin-based CD1 donor opens a new platform for exploring the biology of HNO.

NiS-modified zeolite imidazolic acid frame-67 as a bi-functional catalyst: A non-enzymatic lactic acid sensor and supercapacitor

The ZIF-67/NiS composite electrode was prepared on nickel foam (NF) matrix by hydrothermal method. NiS has been widely studied in sensors and supercapacitors due to its good electron transfer ability and good pseudocapacitor performance. Therefore, we prepared ZIF-67/NiS composite electrode. The synthesised ZIF-67/NiS composite electrode not only has certain electrochemical performance of battery type electrode, but also is sensitive to lactic acid (LA), and can be used as a non-enzymatic LA sensor and a dual-function material for supercapacitors. The detection limit of LA concentration in alkaline solution is 0.8 μM, and the sensitivity is 1.34 μA μM−1 cm−2. Indicating that the electrode has good electrochemical sensing performance. The GCD test results show that the charging capacity of the ZIF-67/NiS is 2.5 times that of the ZIF-67. The ZIF-67/NiS composite has good cyclic performance, and the capacitance retention rate of the ZIF-67/NiS composite is 87% at 10 A/g current density.

Linker-Preserved Iron Metal-Organic Framework-Based Lateral Flow Assay for Sensitive Transglutaminase 2 Detection in Urine Through Machine Learning-Assisted Colorimetric Analysis.

A groundbreaking demonstration of the utilization of the metal-organic framework MIL-101(Fe) as an exceptionally perceptive visual label in colorimetric lateral flow assays (LFA) is described. This pioneering approach enables the precise identification of transglutaminase 2 (TGM2), a recognized biomarker for chronic kidney disease (CKD), in urine specimens, which offers a remarkably sensitive naked-eye detection mechanism. The surface of MIL-101(Fe) was modified with oxalyl chloride, adipoyl chloride, and poly(acrylic) acid (PAA); these not only improved the labeling material stability in a complex matrix but also achieved a systematic control in the detection limit of the TGM2 concentration using our LFA platform. The advanced LFA with the MIL-101(Fe)-PAA label can detect TGM2 concentrations down to 0.012, 0.009, and 0.010 nM in Tris-HCl buffer, urine, and desalted urine, respectively, which are approximately 55-fold lower than those for a conventional AuNP-based LFAs. Aside from rapid TGM2 detection (i.e., within 20 min), the performance of the MIL-101(Fe)-PAA-based LFA on reproducibility [coefficients of variation (CV) < 2.9%] and recovery (95.9-103.2%) along with storage stability within 25 days of observation (CV < 6.0%) shows an acceptable parameter range for quantitative analysis. A sophisticated sensing method grounded in machine learning principles was also developed, specifically aimed at precisely deducing the TGM2 concentration by analyzing immunoreaction sites. More importantly, our developed LFA offers potential for clinical measurement of TGM2 concentration in normal human urine and CKD patients' samples.

Silver-palladium bimetallic nanoparticles stabilized by elm pod polysaccharide with peroxidase-like properties for glutathione detection and photothermal anti-tumor ability

Noble metal nanoparticles show good application prospects in biosensors and anti-tumor drug research. Herein, the near-spherical silver‑palladium bimetallic nanoparticles supported by elm pod polysaccharide (EPP-AgPd1.5 NPs) were prepared by using the elm pod polysaccharide (EPP). EPP acts as a stabilizer and reducing agent due to its water solubility and weak reducing ability. The particle size of EPP-AgPd1.5 NPs was 33.6 ± 5.5 nm. In addition, EPP-AgPd1.5 NPs had peroxidase-like activity to catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) to oxidized TMB by catalyzing H2O2 to OH. Based on the peroxidase-like activity of EPP-AgPd1.5 NPs, a method for detecting glutathione was established, and the detection limit and linear range of glutathione concentration were 0.279 μM and 0–400 μM, respectively. More importantly, the photothermal conversion efficiency of EPP-AgPd1.5 NPs reached 39.7 %, and their inhibition rate in HeLa cells reached 69.9 %. Silver‑palladium bimetallic nanoparticles stabilized by EPP had good performance in glutathione detection and anti-tumor drugs.

Selective determination of an ovarian cancer biomarker at low concentrations with surface imprinted nanotube based chemosensor

In this study, an electrochemical chemosensor that utilizes a conductive polymer-based molecularly imprinted polymer (MIP) surface for rapid and reliable determination of CA125 was devised. A novel method has been applied to fabricate CA125 imprinted polypyrrole nanotubes (MI-PPy NT) via vapor deposition polymerization (VDP) as a recognition element for highly selective and sensitive determination of CA125. The chemosensor was prepared by immobilizing MI-PPy NT onto screen-printed gold electrodes (Au-SPE) and the performance of the sensor was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in terms of selectivity, sensitivity, linear dynamic concentration range (LDR) and limit of detection (LOD). The MI-PPy NT@Au-SPE sensor exhibited high sensitivity (68.57 μA per decade) to the CA125 concentration ranging from 0.1 U mL−1 to 100 U mL−1 at an LOD of 0.4 U mL−1 with a correlation coefficient of 0.9922. The developed chemosensors with their novel design combined with a facile fabrication method, prove to be promising as future state-of-the-art biosensors.

Chemical surface modification of carbon dots with Germanium: A highly sensitive and selective ratiometric fluorescence probe for Mg2+ detection using DFT and TD-DFT

In this study, we chemically modified carbon dots (Cdots) using germanium, enhancing their sensitivity and selectivity as a ratiometric fluorescence probe for precise detection of Mg2+ ions. Excitation of the modified Cdots resulted in a distinct emission peak at 527 nm, enabling accurate measurement of Mg2+ concentrations across a linear range. The surface modification with germanium led to the creation of novel emitting centers on the Cdots' surface. Theoretical calculations using density functional theory (DFT) revealed the effective suppression of these emitting centers through a photo-induced electron transfer (PET) process, utilizing the nitrogen lone pair electrons on the Cdots' surface. Furthermore, adjacent Cdots' surface pyrazino[2,3-f][1,10]-phenanthroline (PPT) nitrogen atoms formed chemical bonds with Mg2+ ions, resulting in the formation of aggregated Cdots. Consequently, the intricate complexation terminated the PET process, resulting in a novel emission peak at longer wavelengths. This study presents a highly sensitive and selective ratiometric fluorescent detection system with exceptional low concentration detection limit for precise Mg2+ ion detection.

Review of recent advances and sensing mechanisms in solid-state organic thin-film transistor (OTFT) sensors

Advances in processing of active layers of organic thin-film transistor (OTFT)-based chemical and biological sensors have enabled significant developments in their performance, achieving part-per-billion molar concentration limits of detection.

High-sensitivity detection of low-concentration heavy metal ions in solution by multiple reflection enhanced absorption (MREA) spectroscopy.

Heavy metal ions (Cr6+, Co2+, Ni2+, and Cu2+) in the electroplating and electrolysis industries are significantly related to process parameters and product quality, even at lower concentrations. Absorption spectroscopy is widely used for substance qualitative and quantitative analysis, which is an analytical method with the potential for real-time monitoring of heavy metal ions concentration in industrial processes. In this paper, a low-concentration heavy metal ion analysis method based on multiple reflection enhanced absorption (MREA) is proposed. Compared with traditional absorption, MREA has the advantages of low concentration detection limit and high-sensitivity. First, a reflective film (Al-SiO2) was prepared and a multiple reflection optical structure was designed to realize multiple parallel reflections of light in the solution medium. Then absorption spectra of low-concentration Cr6+, Co2+, Ni2+ and Cu2+ solutions were measured by MREA and traditional absorption methods. Finally, spectral bandwidth and incident light spots were optimized to obtain a superior absorption enhancement effect. The results showed that MREA could effectively increase the substance absorbance compared with traditional absorption. At the same time, with the optimal spectral bandwidth (0.4 nm) and incident light spot (1 mm), the detection limit of Cr6+, Co2+, Ni2+ and Cu2+ was reduced by 81.48%, 82.52%, 80.92% and 82.93%, respectively. The sensitivity was improved by 5-6 times, which was more obvious for low-concentration detection. In addition, the MREA method can achieve ion concentration analysis when Cr6+, Co2+, Ni2+, and Cu2+ coexist, and the linear correlative coefficients of the C-A curves were all greater than 0.999. Moreover, by adjusting reflectivity of the reflective film and the number of reflections in the optical structure, the results of the MREA method can be further optimized for the low-concentration heavy metal ion analysis. The MREA method has the advantages of simplicity, rapidity and versatility, which can provide the technical foundation for real-time monitoring method development of low-concentration heavy metal ions in industrial processes.

Resonance-Assisted Surface-Enhanced Raman Spectroscopy Amplification on Hierarchical Rose-Shaped MoS2/Au Nanocomposites.

Surface-enhanced Raman spectroscopy (SERS) has emerged as a highly sensitive trace detection technique in recent decades, yet its exceptional performance remains elusive in semiconductor materials due to the intricate and ambiguous nature of the SERS mechanism. Herein, we have synthesized MoS2 nanoflowers (NFs) decorated with Au nanoparticles (NPs) by hydrothermal and redox methods to explore the size-dependence SERS effect. This strategy enhances the interactions between the substrate and molecules, resulting in exceptional uniformity and reproducibility. Compared to the unadorned Au nanoparticles (NPs), the decoration of Au NPs induces an n-type effect on MoS2, resulting in a significant enhancement of the SERS effect. This augmentation empowers MoS2 to achieve a low limit of detection concentration of 2.1 × 10-9 M for crystal violet (CV) molecules and the enhancement factor (EF) is about 8.52 × 106. The time-stability for a duration of 20 days was carried out, revealing that the Raman intensity of CV on the MoS2/Au-6 substrate only exhibited a reduction of 24.36% after undergoing aging for 20 days. The proposed mechanism for SERS primarily stems from the synergistic interplay among the resonance of CV molecules, local surface plasma resonance (LSPR) of Au NPs, and the dual-step charge transfer enhancement. This research offers comprehensive insights into SERS enhancement and provides guidance for the molecular design of highly sensitive SERS systems.

Multigas nonresonant photoacoustic spectroscopy sensor based on a broadband radiation source

AbstractMultigas detection is in demand for a wide range of environmental and industrial applications. In this work, a sensitive and selective multigas photoacoustic spectroscopy (MG‐PAS) sensor was developed by employing a nonresonant photoacoustic spectroscopy technique combining a broadband radiation source. Six gases including CO, CO2, CH4, C2H2, C2H4, and C2H6 were selected as target measurement molecules. Selectivity of the MG‐PAS was realized by using six mid‐infrared narrow‐band filters which integrated in a homemade filter wheel. A minimum concentration detection limits of 0.2 ppm for CO, 0.05 ppm for CO2, 0.12 ppm for CH4, 0.1 ppm for C2H2, 0.81 ppm for C2H4, and 0.05 ppm for C2H6 were obtained, respectively, with a 1‐s integration time. Measurements of six gas mixtures showed that the average measurement error of the MG‐PAS sensor was within 2%.

Coupling capillary electrophoresis with mass spectrometry for the analysis of oxidized phospholipids in human high-density lipoproteins.

The oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (ox-PAPC) products in human high-density lipoproteins (HDLs) were investigated by low-flow capillary electrophoresis-mass spectrometry (low-flow CE-MS). To accelerate the optimization, native PAPC (n-PAPC) standard was first analyzed by a commercial CE instrument with a photodiode array detector. The optimal separation buffer contained 60% (v/v) acetonitrile, 40% (v/v) methanol, 20mM ammonium acetate, 0.5% (v/v) formic acid, and 0.1% (v/v) water. The selected separation voltage and capillary temperature were 20kV and 23°C. The optimal CE separation buffer was then used for the low-flow CE-MS analysis. The selected MS conditions contained heated capillary temperature (250°C), capillary voltage (10V), and injection time (1 s). No sheath gas was used for MS. The linear range for n-PAPC was 2.5-100.0µg/mL. The coefficient of determination (R2 ) was 0.9918. The concentration limit of detection was 1.52µg/mL, and the concentration limit of quantitation was 4.60µg/mL. The optimal low-flow CE-MS method showed good repeatability and sensitivity. The ox-PAPC products in human HDLs were determined based on the in vitro ox-PAPC products of n-PAPC standard. Twenty-one ox-PAPC products have been analyzed in human HDLs. Uremic patients showed significantly higher levels of 15 ox-PAPC products than healthy subjects.

Heterostructured organic/MoS2 nanowall with synergistic SERS enhancement enabling direct and sensitive detection of contaminants

In recent years, the π-conjugated organic molecular system has attracted considerable attention for its surface-enhanced Raman scattering (SERS) properties. However, the practical application of π-conjugated organic materials as SERS substrates is limited due to the inefficient dissociation of excitons, weak enhancement, and poor reproducibility. Herein, we proposed a novel nanowall SERS heterocomposite based on 3D D(C7CO)-BTBT nanowalls and 2D few-layer MoS2 flakes. A significant SERS activity of the D(C7CO)-BTBT/MoS2 nanowall heterocomposite can be achieved by the charge transfer (CT) resonance enabled by the π-conjugated interactions between D(C7CO)-BTBT and MoS2 and the electromagnetic field spatial distribution induced by the D(C7CO)-BTBT nanowalls. The concentration limit of detection (LOD) of the methylene blue (MB) molecules absorbed on the heterostructured D(C7CO)-BTBT/MoS2 nanowall substrate is as low as 8.2 × 10−11 M, which is excellent among the reported organic-based substrates. A practical SERS detection for the 100 nm polystyrene (PS) nanoparticles on the D(C7CO)-BTBT/MoS2 substrates can be down to 4.5 × 105 ng/L, which is exceptional for the real-time monitoring of emerging contaminants based on SERS technology. This research not only provides a new SERS enhancement strategy for organic-based materials, but also may be helpful in exploring a potential candidate for SERS detection of emerging contaminants.

Carbon Paste Electrode Modified by Dibenzo 18-crown-6 for the Determination of Pb in Carrot Using Differential Pulse Voltammetry

In this research, the modification of carbon paste electrode (CPE) using dibenzo 18-crown-6 was carried out to detect Pb level in carrot. The purpose of this electrode modification is to increase the sensitivity of the measurement. The optimized parameters were scan rate, composition of dibenzo 18-crown-6 in carbon paste, and supporting electrolyte. Measurements were validated by determining the linear concentration range, detection limit (LoD), quantification limit (LoQ), repeatability, selectivity, and recovery. At the best measurement conditions, the modified CPE (CPE-Dbc) was applied to determine Pb in carrot. The optimum measurements conditions were obtained the optimum concentration of crown ether in carbon paste was 0.8%, the scan rate using CPE at 15 mV/s, increased to 20 mV/s, and H2SO4 solution as supporting electrolyte. The linear concentration was found in the range of 5-100 µg/L using CPE and became wider to 5-2000 µg/L using CPE-Dbc. The values of LoD and LoQ measurement using CPE were 0,3575 µg/L and 0,3583 µg/L, and decreased to 0,1265 µg/L and 0,1266 µg/L using CPE-Dbc. CPE and CPE-Dbc had good precision with Horwitz ratio values were 0,2231 and 0,2183, which is smaller than two. The percentage of recovery of Pb in the mixture of standard and sample solutions was (88,97 ± 2,76)%. The presence of Cu, Cd and Na in the solution did not interfere the measurement of Pb. The concentration of Pb in carrot sample was (1,8423 ± 0,0002) mg/kg, which was higher than the acceptable concentration according to SNI No. 7387:2009, which is 0,5 mg/kg.

Silver nanosheets self-assembled on polystyrene microspheres to form “hot spots” with different nanogap distances for high sensitive SERS detection

Herein, we reported a facile method to control the nanogap distance of silver (Ag) nanosheets to obtain high sensitive plasmonic Surface-enhanced Raman scattering (SERS) substrates. The sulfonated polystyrene (SPS) microspheres with different diameters were first fabricated using micro-emulsion synthesis, and then the SPS microspheres were coated with Ag nanosheets through chemical synthesis with citric acid/ascorbic acid to form Ag nanosheets@SPS (Ag@SPS) substrates with different nanogap distances. The results showed that the nanogap distance of Ag nanosheets self-assembled on SPS microspheres reduced from 80-150 nm to 28–68 nm when the diameter of SPS microspheres increased from 0.9 to 3.5 μm, and the enhancement factor (EF) increased from 105 to 107, the limit of detection of rhodamine 6G (R6G) for the Ag@SPS microspheres reduced from 10−10 to 10−13 mol/L. It confirmed that the Ag nanosheets coated on the surface of SPS microspheres could achieve ultra trace detection of analyte. Furthermore, the low concentration detection limit for melamine with the Ag@SPS microspheres substrate was about 10−8 mg/L, which is lower than the standard legislated by the European Union and the Food & Drug Administration. In addition, the SERS spectrum of 3-mercaptopropionic acid (3-MPA) could be also detected when its concentration was 10−8 mol/L. The prepared substrate offered a promising opportunity for SERS practical applications.