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Rapid, sensitive, point-of-care detection of pathogenic bacteria is important for food safety. In this study, we developed a novel quantum dot nanobeads-labelled lateral flow immunoassay strip (QBs-labelled LFIAS) combined with strand displacement loop-mediated isothermal amplification (SD-LAMP) for quantitative Salmonella Typhimurium (ST) detection. Quantum dot nanobeads (QBs) served as fluorescence reporters, providing good detection efficiency. The customizable strand displacement (SD) probe was used in LAMP to improve the specificity of the method and prevent by-product capture. Detection was based on a sandwich immunoassay. A fluorescence strip reader measured the fluorescence intensity (FI) of the test (T) line and control (C) line. The linear detection range of the strip was 102–108 CFU·mL−1. The visual limit of detection was 103 CFU·mL−1, indicating that the system was 10-fold more sensitive than AuNPs-labelled test strips. ST specificity was analyzed in accordance with agarose gel outputs of PCR and SD-LAMP. We detected ST in foods with an acceptable recovery of 85%–110%. The method is rapid, simple, almost equipment-free, and suitable for bacterial detection in foods and for clinical diagnosis.

Owing to frequent environmental monitoring of tetrabromobisphenol-A (TBBPA) analogs and their potential ecotoxicological effects on organisms, analysis of trace levels of TBBPA analogs with more non-polar and less water-soluble characteristics is of great significance for studying their environmental behaviors and toxic effects. Herein, a fast and sensitive technique is developed for directly detecting aqueous TBBPA analogs, including TBBPA mono(allyl ether) (TBBPA-MAE), TBBPA mono(2,3-dibromopropyl ether) (TBBPA-MDBPE), TBBPA mono(2-hydroxyethyl ether) (TBBPA-MHEE) and TBBPA mono(glycidyl ether) (TBBPA-MGE), by combining solid phase microextraction (SPME) based on porous covalent organic frameworks (Porous-COFs) with constant flow desorption ionization-mass spectrometry (CFDI-MS). As chromatographic separation is replaced by constant flow desorption, each sample can be analyzed within 7 min. The hierarchical porous structures (microporous, mesoporous and macroporous) of COFs lead to the enhanced mass transfer and the easier accessibility of active sites to TBBPA analogs, so that the extraction efficiency is 2.3–3.6 times higher than pure microporous COFs, and far superior to commercial coatings. The detection limit and quantification limit of this method are 0.1–1 and 0.4–3.2 ng/L, respectively. Ultra-trace levels of TBBPA analogs from 5.0 to 66 ng/L have been successfully detected in river and sea water samples, showing great potential for subsequent studies of their environmental behaviors and toxicological effects

The rapid and sensitive detection of 2,6-pyridinedicarboxylic acid (DPA), one of the main biomarkers of Bacillus anthracis, is of great significance for the screening and diagnosing of anthrax. Herein, a ratiometric fluorescent nanoprobe based on zeolite imidazolate framework-8 (ZIF-8)@AuNCs-Tb was constructed by embedding both gold nanoclusters (AuNCs) and terbium ions (Tb3+) into ZIF-8 for high-resolution visual detection of DPA. Due to the aggregation induced emission enhancement (AIE) effect, AuNCs embedded in ZIF-8 emit a strong orange fluorescence. When Tb3+ is coordinated with DPA added to the nanoprobe, it will emit a strong green fluorescence owing to the antenna effect. The results reveal that ZIF-8@AuNCs-Tb nanoprobe can detect DPA effectively with a good linear relationship in the range of 40–200 and 200–1000 μmol/L, the limit of detection (LOD) is estimated at 1.8 μmol/L (3σ/k). The proposed nanoprobe shows a remarkable selectivity for DPA and is quite easy to realize visualization based on the fluorescent color changing from orange to green, which has potential application in clinical diagnosis. The feasibility of this method was verified by standard addition recovery experiments simulating the release of DPA from spores.

By exchanging the conventional role of functional monomer and template molecules, we develop a new molecularly imprinted nanospheres with grape grain structures based on multi-hydrogen bonding interactions between melamine and 6-aminouracil. Molecular imprinting-electrochemical sensor was established with the assistance of graphene and ionic liquids. The content of melamine in dairy products was detected by the molecular imprinting-electrochemical sensor. The detection limit was determined to be as low as 1.57 × 10−3 mg kg−1.

Introduction Mycotoxins are toxic metabolites produced by fungi that commonly contaminate foods. As recommended by the World Health Organization, total diet study (TDS) is the most efficient and effective way to estimate the dietary intakes of certain chemical substances for general populations. It requires sensitive and reliable analytical methods applicable to a wide range of complex food matrices and ready-to-eat dishes. Objectives A novel strategy with high selectivity and sensitivity, incorporating three methods based on ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), was designed for measuring 43 mycotoxins in dietary samples in a China TDS. Methods The 43 mycotoxins were divided into 3 groups for analysis to achieve better performance. For each group, an UHPLC-MS/MS method was developed to determine the target compounds after clean-up by solid phase extraction. A total of 21 isotope internal standards were employed for accurate quantitation. Method validation in terms of linearity, selectivity, sensitivity, accuracy, and precision was performed for all the 43 mycotoxins in 12 complex food matrices. Results The limits of detection (LODs) and limits of quantitation (LOQs) were 0.002–1 ng mL−1 and 0.006–3 ng mL−1, respectively. The method recoveries of the 43 mycotoxins spiked in 12 food categories were in the range of 60.3%–175.9% after internal standard correction, with relative standard deviations (RSDs) below 13.9%. For practical application, this method was utilized for 72 dietary samples collected from 6 provinces in the 6th China TDS. More than 80% of the samples were found contaminated by mycotoxins. DON, SMC, FB1, ZEN, BEA, ENNB1, and ENNB were most detected. Conclusions The proposed methods with high sensitivity, accuracy, and robustness provide powerful tools for multi-mycotoxin monitoring and dietary exposure assessment, allowing 43 mycotoxins, including some emerging mycotoxins, to be accurately investigated in a total diet study for the first time.

The development of uranyl ion detection technology has exhibited its significance in public security and environmental fields for the radioactivity and chemical toxicity of uranyl ion. The WHO standard of uranyl ion makes it necessary to develop highly sensitive uranyl rapid warning system in drinking water monitoring. Herein, a visualized rapid warning system for trace uranyl ion is carried out based on electrochemiluminescence (ECL) imaging technology to give an ultra-low limit of detection (LOD) and high selectivity. Amidoxime, a bi-functional group with both uranyl ion capturing and co-reactive functions, is modified on a conjugated polymer backbone with strong ECL signal to be prepared into three-in-one polymer nanoparticles (PNPs) with self-enhanced ECL property. The captured uranyl ion can enhance the ECL signal of PNPs via resonance energy transfer process to give the LOD as 0.5 ng/L, which is much lower than the known luminescent uranyl sensors. Furthermore, ECL imaging technology is introduced into realizing visualized uranyl rapid warning, and can be successfully applied on natural water samples. This study provides a novel strategy for uranyl rapid warning, and shows its potential meaning in public security and environmental fields.

As the most commonly used antipyretic and analgesic drug, paracetamol (PA) coexists with neurotransmitter dopamine (DA) in real biological samples. Their simultaneous determination is extremely important for human health, but puzzled by their mutual interference. In order to improve the conductivity, adsorption affinity, sensitivity and selectivity of TiO2-based electrochemical sensor, N-doped carbon@TiO2 double-shelled hollow sphere (H–C/N@TiO2) is designed and synthesized by simple alcoholic and hydrothermal method, using polystyrene sphere (PS) as a template. Meanwhile, TiO2 hollow spheres (H–TiO2) or N-doped carbon hollow spheres (H–C/N) are prepared by the same method. H–C/N@TiO2 hollow spheres have good conductivity, charge separation, and the highly enhanced and stable current responses for the detection of PA and DA. The detection limit and linear range are 50.0 nmol/L and 0.3–50 μmol/L for PA, 40.0 nmol/L and 0.3–50 μmol/L for DA, respectively, which are better than those of carbon-based sensors. Moreover, this electrochemical sensor with high selectivity, strong anti-interference, high reliability, and long time durability, can be used for the simultaneous detection of PA and DA in human blood serum and saliva. The high electrochemical performance of H–C/N@TiO2 is attributed to the multi-functional combination of different layers, because of good conductivity, absorption and electrons transfer ability from in-situ N-doped carbon and electrocatalytic activity from TiO2.

Iron chalcogenides have attracted great interest as potential substitutes of nature enzymes in the colorimetric biological sensing due to their unique chemodynamic characteristics. Herein, we reported the preparation of ultrathin FeS nanosheets (NSs) by a simple one-pot hydrothermal method and the prepared FeS NSs exhibit strong Fenton-reaction activity to catalyze hydrogen peroxide (H2O2) for generation of hydroxyl radical (•OH). Based on the chromogenic reaction of resultant •OH with 3,3′,5,5′-tetramethylbenzidine (TMB), we develop colorimetric biosensors for highly sensitive detection of H2O2 and glutathione (GSH). The fabricated biosensors show wide linear ranges for the detection of H2O2 (5-150 μmol/L) and GSH (5-50 μmol/L). Their detection limits for H2O2 and GSH reach as low as 0.19 μmol/L and 0.14 μmol/L, respectively. The experimental results of sensing intracellular H2O2 and GSH demonstrate that this colorimetric method can realize the accurate detection of H2O2 and GSH in normal cells (LO2 and 3T3) and cancer cells (MCF-7 and HeLa). Our results have demonstrated that the synthesized FeS NSs is a promising material to construct colorimetric biosensors for the sensitive detection of H2O2 and GSH, holding great promising for medical diagnosis in cancer therapy.

Rapid screening of foodborne pathogens is of great significance to ensure food safety. A microfluidic biosensor based on immunomagnetic separation, enzyme catalysis and electrochemical impedance analysis was developed for rapid and sensitive detection of Salmonella typhimurium. First, the bacterial sample, the magnetic nanoparticles (MNPs) modified with capture antibodies, and the enzymatic probes modified with detection antibodies and glucose oxidase (GOx) were simultaneously injected into the microfluidic chip, followed by mixing and incubation to form MNP-bacteria-probe sandwich complexes. Then, glucose with high impedance was injected into the chip and catalyzed by the GOx on the complexes into hydrogen peroxide with high impedance and gluconic acid with low impedance, which was finally measured using the low-cost interdigitated microelectrode and the electrochemical impedance analyzer to determine the target bacteria. Under the optimal conditions, this biosensor could quantitatively detect Salmonella typhimurium at the concentrations from 1.6 × 102 CFU/mL to 1.6 × 106 CFU/mL in 1 h with the low detection limit of 73 CFU/mL. Besides, this biosensor was demonstrated with good feasibility for practical applications by detecting the Salmonella typhimurium spiked chicken meat samples.

A gold nanoparticle (AuNP) aggregation-induced colorimetric aptasensing method for quantitative detection of sulfadimethoxine (SDM) with a smartphone was developed. AuNPs were complexed with aptamers which protected AuNPs from aggregating in high-concentration salt solutions. In the presence of SDM, SDM bound with the aptamer on the surface of AuNPs with higher affinity, which competitively desorbed the aptamer from the AuNP surface and resulted in AuNPs aggregation, accompanied with a color change from red to purple-blue. The R, G and B values of images taken by a smartphone camera were analyzed with an app on the smartphone, and were utilized for quantitative analysis of SDM. Under the optimized conditions, the colorimetric aptasensing method using a smartphone showed high sensitivity for SDM, with the limit of detection of 0.023 ppm, lower than the allowed maximum SDM residue limit. This study provides a simple, fast, and easy to read method for on-site quantitative biochemical and cellular analysis.

In recent years, various methods for detecting exogenous and endogenous hypochlorite have been studied, considering its essential role as a biomolecule. However, the existing technologies still pose obstacles such as their invasiveness, high costs, and complicated operation. In the current study, we developed a glow-type chemiluminescent probe, hypochlorite chemiluminescence probe (HCCL)-1, based on the scaffold of Schaap's 1,2-dioxetane luminophores. To better explore the physiological and pathological functions of hypochlorite, we modified the luminophore scaffold of HCCL-1 to develop several probes, including HCCL-2, HCCL-3, and HCCL-4, which amplify the response signal of hypochlorite. By comparing the luminescent intensities of the four probes using the IVIS® system, we determined that HCCL-2 with a limit of detection of 0.166 μM has enhanced sensitivity and selectivity for tracking hypochlorite both in vitro and in vivo.

Enzyme assisted DNA probes are powerful tools in molecular diagnostics for their simplicity, rapidity, and low detection limit. However, cost of probes, difficulty in optimization and disturbance of secondary structure hindered the wider application of enzyme assisted DNA probes. To solve the problems, we designed a new system named shared-probe system. By introducing two unlabeled single stranded DNA named Sh1 and Sh2 as the bridge between probe and the substrate, the same sequence of dually labeled probe with stable performance was shared for different mutations, thus sparing the expense and time cost on designing, synthesizing and optimizing corresponding probes. Besides, the hybridization between Sh1 and the substrate could overcome secondary structures, which guaranteed the detection of different substrates. The performance and generality of the design were tested by low abundance detection in synthetic single DNA samples and the limit of detection was 0.05% for PTENR130Q, EGFR-L858R and 0.02% for BRCA1-NM007294.3. In genomic DNA samples, the limit of detection of 0.1% can be achieved for EGFR-L858R, demonstrating the potential of clinical application in our design.

Rutin, a flavonoid found in fruits and vegetables, is a potential anticancer compound with strong anticancer activity. Therefore, electrochemical sensor was developed for the detection of rutin. In this study, CoWO4 nanosheets were synthesized via a hydrothermal method, and porous carbon (PC) was prepared via high-temperature pyrolysis. Successful preparation of the materials was confirmed, and characterization was performed by transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. A mixture of PC and CoWO4 nanosheets was used as an electrode modifier to fabricate the electrochemical sensor for the electrochemical determination of rutin. The 3D CoWO4 nanosheets exhibited high electrocatalytic activity and good stability. PC has a high surface-to-volume ratio and superior conductivity. Moreover, the hydrophobicity of PC allows large amounts of rutin to be adsorbed, there by increasing the concentration of rutin at the electrode surface. Owing to the synergistic effect of the 3D CoWO4 nanosheets and PC, the developed electrochemical sensor was employed to quantitively determine rutin with high stability and sensitivity. The sensor showed a good linear range (5–5000 ng/mL) with a detection limit of 0.45 ng/mL. The developed sensor was successfully applied to the determination of rutin in crushed tablets and human serum samples.

We herein proposed a sample introduction technique based on solution cathode glow discharge (SCGD) of a portable design for inductively coupled plasma-optical emission spectrometry (ICP-OES) and its application in sensitive determination of mercury. The products from SCGD containing mercury vapor, were transported by an Ar flow to ICP spectrometer for detection. A gas liquid separator (GLS) and a dryer were used to condense and remove most of the accompanying moisture, which greatly improved both the stability and sensitivity of the signal. The detection limit (DL) acquired by this developed method was 0.22 μg/L (194.1 nm), which was nearly 82 times lower than that obtained by pneumatic nebulization (PN). The relative standard deviation (RSD) was 1.4% (n = 14) for a 50 μg/L standard. Blank solution (HNO3, pH 1) can effectively elute mercury residue. Its accuracy and practicality were also demonstrated by the determination of GBW10029 (fish) certified reference material, shrimp, crawfish, soil and human hair samples. The results showed good consistency with the certified values and the values obtained using inductively coupled plasma−mass spectrometry.

An organic-inorganic hybrid FeIII–PrIII-included 2-germano-20-tungstate [Pr(H2O)8]2H2[Fe4(H2O)4 (pca)4Ge2W20O72]•34H2O (Hpca = 2-pyridinecarboxylic acid) (1) was hydrothermally prepared. Its polyoxoanion comprises one tetra-FeIII incorporated [Fe4(H2O)4(pca)4Ge2W20O72]8- hybrid entity and two [Pr(H2O)8]3+ ornamental cations. The [Fe4(H2O)4(pca)4Ge2W20O72]8- 2-germano-20-tungstate entity can be regarded as an infrequent S-type [Ge2W20O72]16- cluster pocketed by four [Fe(H2O)(pca)]2+ cations. The S-type [Ge2W20O72]16- cluster could be imagined as condensation of two divacant Keggin [α-GeW10O37]10- segments by sharing two atoms. It is of interest is that carboxyl O and pyridine N atoms on pca ligands concurrently bind with Fe3+ cations in a five-membered heterocyclic fashion to increase the stability of the whole structure. Furthermore, the electrochemical biosensing properties of 1 as the modified electrode material have been investigated for detecting norepinephrine (NPP), showing a low detection limit of 3.25 μmol/L. This work not only enriches structures of heterometallic germanotungstates (GTs), but also expands applications of polyoxometalates (POMs) in the electrochemical biosensing field.

A simple and efficient dithizone-functionalized solid-phase extraction (SPE) procedure, online coupled with high-performance liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry, was developed for the first time for enrichment and determination of ultra-trace mercury (Hg) species (inorganic divalent Hg (Hg(II)), methylmercury (CH3Hg(II)) and ethylmercury (C2H5Hg(II)) in cereals and environmental samples. In the proposed method, functionalization of the commercial C18 column with dithizone, enrichment, and elution of the above Hg species can be completed online with the developed SPE device. A simple solution of 2-mercaptoethanol (1% (V/V)) could be used as an eluent for both the SPE and HPLC separation of Hg species, significantly simplifying the method and instrumentation. The online SPE method was optimized by varying dithizone dose, 2-mercaptoethanol concentration, and sample volume. In addition, the effect of pH, coexisting interfering ions, and salt effect on the enrichment was also discussed. Under the optimized conditions, the detection limits of Hg species for 5 mL water sample were 0.15 ng/L for Hg(II), 0.07 ng/L for CH3Hg(II), and 0.04 ng/L for C2H5Hg(II) with recoveries in the range of 85%–100%. The developed dithizone-functionalized C18 SPE column can be reused after a single functionalization, which significantly simplifies the enrichment step. Moreover, the stability of Hg species enriched on the SPE column demonstrated its suitability for field sampling of Hg species for later laboratory analysis. This environment-friendly method offers a robust tool to detect ultra-trace Hg species in cereals and environmental samples.

The protein complex of recombinant human insulin-like growth factor-1 and insulin‑like growth factor binding protein‑3 (rhIGF-1/rhIGFBP-3; mecasermin rinfabate), is an investigational product for the prevention of complications of prematurity. Delivery of rhIGF-1/rhIGFBP-3 is by continuous central line intravenous infusion in preterm infants until endogenous IGF-1 production begins. Protein-specific analytical methodologies were developed to evaluate the compatibility of rhIGF- 1/rhIGFBP-3 at low protein concentrations (∼2.5-10 μg/mL) expected when co-administered with other required medications in the NICU. Highly sensitive detection of the biologic potential degradants (fragments) and/or molecular modifications (oxidized species, aggregates) required the use of reversed-phase high-performance liquid chromatography and size-exclusion ultra-performance liquid chromatography coupled with mass spectrometric detection. We report on the quantification of rhIGF-1/rhIGFBP-3, its components and degradants, to a limit of quantitation of 3.1 μg/mL upon mixing with 24 commonly administered neonatal medications. Methods developed for the rhIGF-1/rhIGFBP-3 admixtures, optimized in studies with furosemide, caffeine citrate and ampicillin, demonstrated good reproducibility, linearity, and limit of detection/quantitation. Using these methods, no increase in degradation of rhIGF-1/rhIGFBP-3 components and no increase in oxidation or aggregation level was observed with caffeine citrate, while admixtures of rhIGF-1/rhIGFBP-3 with ampicillin yielded lower mass recovery of rhIGF-1/rhIGFBP-3 components, which likely resulted from adduct formation. Furosemide was found to be physically incompatible with rhIGF-1/rhIGFBP-3. Our findings support the use of these methodologies for detection of protein modifications under various clinical administration conditions, and additionally supplement physical compatibility data studies of ultra-low concentrations of rhIGF-1/rhIGFBP-3 post co-administration to preterm infants with other medications (manuscript in-preparation).

Indole-3-carbinol (I3C), an important anticancer compound found in broccoli, has attracted considerable attention. The rapid extraction and accurate analysis of I3C in the pharmaceutical industry in broccoli is challenging as I3C is unstable at low pH and high temperature. In this study, a rapid, accurate, and low-cost ultrasound-assisted dispersive-filter extraction (UADFE) technique based on poly(deep eutectic solvent)-graphene oxide (PDES-GO) adsorbent was developed for the isolation and analysis of I3C in broccoli for the first time. PDES-GO with multiple adsorption interactions and a fast mass transfer rate was synthesized to accelerate adsorption and desorption. UADFE was developed by combining dispersive solid-phase extraction (DSPE) and filter solid-phase extraction (FSPE) to realize rapid extraction and separation. Based on the above two strategies, the proposed PDES-GO-UADFE method coupled with high-performance liquid chromatography (HPLC) allowed the rapid (15–16 min), accurate (84.3–96.4%), and low-cost (adsorbent: 3.00 mg) analysis of I3C in broccoli and was superior to solid-phase extraction, DSPE, and FSPE methods. The proposed method showed remarkable linearity (r=0.9998; region: 0.0840–48.0 μg/g), low limit of quantification (0.0840 μg/g), and high precision (relative standard deviation ≤ 5.6%). Therefore, the PDES-GO-UADFE-HPLC method shows significant potential in the field of pharmaceutical analysis for the separation and analysis of anti-cancer compounds in complex plant samples.

Compared with other transition metal Mxene derived quantum dots (MQDS), Ta-based Mxene quantum dots have good functionality, but Ta-based Mxene quantum dots and their applications have not been studied so far. In this paper, we report for the first time the synthesis of high fluorescence quantum yield (QY) N-doped Ta4C3 quantum dots (N-MQDs) using Ta4C3 quantum dots in acid reflux damaged Ta4C3 nanosheets as precursors and ethylenediamine as nitrogen source. The prepared N-MQDs have excellent blue photoluminescence (PL) properties, particle size is only 2.60 nm, QY is up to 23.4%, and good stability. In addition, it has been reported that N-MQDs can be used as fluorescent probe for detection of Fe3+ and remote force sensing analysis In liquid ion sensing, N-MQDS shows a unique selective quenching of Fe3+ with a detection limit as low as 2 μmol/L, and has great potential as a fast and super-sensitive fluorescent probe for the detection of heavy ion. More importantly, in solid mechanics sensing, the introduction of N-MQDs into self-healing hydrogels can be developed into a fluorescent hydrogel that can be used for accurate remote force measurement and applied in the field of mechanical sensing analysis. Therefore, Ta-based N-MQDs show excellent potential in the field of fluorescence sensing, which provides a door for multi-dimensional sensing of new materials in the future.

Foodborne pathogenic bacteria have been considered as a major risk factor for food safety. It is of great significance to carry out in-field screening of pathogenic bacteria to prevent the outbreaks of foodborne diseases. In this study, a portable lab-on-a-disc platform with a microfluidic disc was developed for rapid and automatic detection of Salmonella typhimurium using a nickel nanowire (NiNW) net for effective separation of target bacteria, horseradish peroxidase nanoflowers (HRP NFs) for efficient amplification of biological signals, and a self-developed smartphone APP for accurate analysis of colorimetric images. First, the microfluidic disc was preloaded with reagents and samples and centrifuged to form one bacterial sample column, one immune NiNW column, one HRP NF column, two washing buffer columns and one tetramethylbenzidine (TMB) column, which were separated by air gaps. Then, a rotatable magnetic field was specifically developed to assemble the NiNWs into a net, which was automatically controlled by a stepped motor to successively pass through the sample column for specific capture of target bacteria, the HRP NF column for specific label of target bacteria, the washing columns for effective removal of sample background and non-specific binding NFs, and the TMB column for colorimetric determination of target bacteria. The color change of TMB from colorless to blue was finally analyzed using the smartphone APP to quantitatively determine the target bacteria. This lab-on-a-disc platform could detect Salmonella typhimurium from 5.6 × 101 CFU/20 μL to 5.6 × 105 CFU/20 μL in 1 h with a lower detection limit of 56 CFU/20 μL. The recovery of target bacteria in spiked chicken samples ranged from 97.5% to 101.8%. This portable platform integrating separation, labeling, washing, catalysis and detection onto a single disc is featured with automatic operation, fast reaction, and small size and has shown its potential for in-field detection of foodborne pathogens.

For determining the accuracy of a calorimeter over the instrument’s entire measuring range, a novel method has been established. For this new approach, (a) benzoic acid (C6H5CO2H) as a Certified Reference Material (CRM), (b) SiO2 and (c) a mixture of CRM benzoic acid and SiO2 have been used. To illustrate the essential difference between 1) the novel analytical method for control of the entire measurement range and 2) the calorimeter calibration, both applications of benzoic acid (BA) have been demonstrated. An experimental result showed that BA was successfully used to check the whole calorimeter measurement range. The results also showed that the same new method was successfully applied to determine the limit of detection and quantification. A new instrument testing process and a new measurement technique have thus been established. In this way, the cost of using CRM to control the accuracy of measuring the entire measuring range of the calorimeter, as shown in this paper, is minimized. The requirements of the ISO/IEC 17025:2017 standard are satisfied.

Excessive mercury ions (Hg2+) in the environment can accumulate in human body along with the food chain to cause serious physiological reactions. The fluorescence probes were considered as convenient tool with great potential for Hg2+ detection. Most existing probes suffer from aggregation-induced quenching (ACQ) effects and insufficient sensitivity. Herein, a novel type of fluorophore was developed by combining the aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT) characteristics. Subsequently, a phenyl thioformate group with photoinduced electron transfer (PET) effect was connected to give an efficient "turn-on" probe (HTM), which exhibited good selectivity toward Hg2+, short response time (30 min), coupled with extremely low detection limit (LOD = 1.68 nmol/L). In addition, HTM was used successfully in real samples, cells and drug evaluation, underlying the superiority of HTM to detect Hg2+ in practical applications.

Rapid and accurate detection of immunoglobulin E (IgE) in serum and reduction of serum dosage are of great significance for clinical detection. Herein, we described a rapid magnetic separation of IgE from patient serum based on Fe3O4@SiO2-NTA@026 sdab as the capture probe and multiple horseradish peroxidase (HRP)-labeled antibodies linked gold nanoparticles (AuNPs) as chemiluminescence (CL) signal amplifier for ultrasensitive detection of total IgE. Results showed that the limit of detection of our immunosensor system in serum samples was 0.03 kU/L, which is lowest in comparison with current methods, and far lower than that of ImmunoCAP for IgE detection (0.1 kU/L). Furthermore, our immunosensor possessed satisfied repeatability and accuracy, as well as good stability. In comparison with the ImmunoCAP for the quantitative detection of IgE, highly consistent results were achieved in 20 serum samples. Specially, this method was also successfully utilized for assessing the IgE traces in breast cancer patients, which provides a new idea for the diagnosis of early cancer. Therefore, we believe that such versatile immunosensor will offer an alternative method for the on-site monitoring and determination of various IgE-related diseases.

The scale of biological discovery is driven by the vessels in which we can perform assays and analyze results, from multi-well plates to microfluidic compartments. We report on the compatibility of sub-nanoliter single-cell containers or “nanovials” with commercial fluorescence activated cell sorters (FACS). This recent lab on a particle approach utilizes 3D structured microparticles to isolate cells and perform single-cell assays at scale with existing lab equipment. Use of flow cytometry led to detection of fluorescently labeled protein with dynamic ranges spanning 2-3 log and detection limits down to ∼10,000 molecules per nanovial, which was the lowest amount tested. Detection limits were improved compared to fluorescence microscopy measurements using a 20X objective and a cooled CMOS camera. Nanovials with diameters between 35-85 µm could also be sorted with purity from 99-93% on different commercial instruments at throughputs up to 800 events/second. Cell-loaded nanovials were found to have unique forward and side (or back) scatter signatures that enabled gating of cell-containing nanovials using scatter metrics alone. The compatibility of nanovials with widely-available commercial FACS instruments promises to democratize single-cell assays used in discovery of antibodies and cell therapies, by enabling analysis of single cells based on secreted products and leveraging the unmatched analytical capabilities of flow cytometers to sort important clones.

Exosomal microRNA (miRNA) is an ideal candidate of noninvasive biomarker for the early diagnosis of cancer. Sensitive and accurate sensing of abnormal exosomal miRNA plays essential role for clinical promotion due to its close correlation with tumor proliferation and progression. Herein, a microfluidic surface-enhanced Raman scattering (SERS) sensor was proposed for an on-line detection of exosomal miRNA based on rolling circle amplification (RCA) and tyramine signal amplification (TSA) strategy. The microfluidic chip consists of a magnetic enrichment chamber, a serpentine fluidic mixer and a plasmonic SERS substrate functionalized with capture probes. The released miRNA activates the capture probe, triggers RCA reaction, and generates a large number of single-stranded DNA products to drive the catalysis of nanotags deposition via TSA, producing numerous “hot spots” to enhance the SERS signals. In merit of the microfluidics chip and nucleic acid-tyramine cascade amplification, the developed SERS sensor significantly improves the sensitivity for the exosomal miRNA assay, resulting in a limit of detection (LOD) as low as 1 pmol/L and can be successfully applied in the analysis of exosomes secreted from breast tumor cells, which demonstrates the potential utility in practical applications.

This work was initiated by synthesizing a carboxylic derivative of Calix[4]resorcinarene through a three step protocol confirmed by proton nuclear magnetic resonance (1H-NMR) spectroscopy and Electrospray ionization mass spectroscopy (ESI-MS). As synthesized derivative, was used as reducing and capping material for the fabrication of small and stable silver nanoparticles (AgNPs) in aqueous medium under the combined influence of dilute alkali and heat at 90°C. These nanoparticles were referred as KM20-AgNPs. Techniques used for characterization of AgNPs include UV-Visible (UV-Vis) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), dynamic light scattering (DLS) and zeta potential analyzer (ZPA). The finally produced KM20-AgNPs were recognized as highly sensitive and extremely selective voltammetric sensor for low level detection of methylene blue drug in the linear working range of 1–30 nM with limit of detection (LOD) and limit of quantification (LOQ) as 0.16 nM and 0.53 nM respectively. The developed sensor was successfully used for sensing of MB in human blood plasma.

The uncontrollable synthesis of Prussian blue (PB) and its weak stability toward OH– are great challenges affecting its electrochemical biosensing application. Herein we utilize the unique properties of chitosan (CS) to realize the facile and controllable synthesis of a CS-PB nanocomposite and combine it with the urease-catalyzed deposition of polydopamine (PDA) for amplifying the electrochemical signal inhibition of PB to develop a novel immunosensing method for protein detection. The immunosensor was constructed on a CS-PB modified electrode, and a urease-functionalized silica nanoprobe was prepared for tracing its sandwich immunoassay toward the model analyte of carcinoembryonic antigen. Besides the electrochemical impedance effect of the quantitatively captured nanoprobes, their enzymatic reaction can release numerous OH– to destroy the PB crystals and also induce the PDA deposition onto the immunosensor. These caused drastic electrochemical signal inhibition to PB. Based on the above multi-signal amplification mechanism, the method exhibits a very low detection limit of 0.042 pg mL–1 along with a very wide linear range of six-order of magnitude. In addition, the CS-PB based immunosensor has excellent specificity, repeatability, stability and reliability. Thus this PB nanocomposite and the proposed electrochemical immunosensing method reveal a promising potential for future applications.

Development of new self-calibrating fluorescent sensing methods has been a popular research field with the aim of protecting the human health and environment sustainability. In this work, a novel Eu-based metal organic framework (MOF) Eu(2,6-NDC)(COO) (BUC-88) was developed by employing 2,6-NDC (2,6-naphthalenedicarboxylic acid) as bridging ligands. BUC-88 performed different sensing process toward quinolone antibiotics and tetracyclines antibiotics in terms of fluorescence intensity and color. BUC-88 exhibited excellent selectivity and sensitivity detection property toward enrofloxacin (ENR), norfloxacin (NOR) and ciprofloxacin (CIP) over other Pharmaceutical and Personal Care Products (PPCPs), accomplishing the detection limit of 0.12 μmol/L, 0.52 μmol/L, 0.75 μmol/L, respectively. Notably, BUC-88 acted as an excellent fluorescence sensor for tetracyclines antibiotics with fast response time (less than 1 s), high selectivity and sensitivity (LODs = 0.08 μmol/L). The fluorescent detection method was successfully used for visual and ultrasensitive detection of ENR, NOR, CIP and tetracycline hydrochloride (TC) in lake water with satisfied recovery from 99.75% to 102.30%. Finally, the photoinduced electron transfer and the competitive absorption of ultraviolet light are the main mechanisms for sensitive detection toward quinolone antibiotics and tetracyclines antibiotics.

Substrate photopatterning has provided versatile applications in biomedical fields. Herein, an universal and efficient photoligation reaction has been used to prepare a patterned capture substrate for a sandwich SERS immunoassay. Photoirradiation induces mild and efficient immobilization of antibodies at the desired region of a gold surface, and the antibody-antigen interaction helps the substrate to capture the antigens in solution specifically. After exposing to SERS probes, i.e., the gold nanoparticles labelled with both antibodies and intrinsically strong Raman reporters, multiple quantitative SERS determination of antigens can be achieved with high sensitivity and specificity. The limit of detection can be as low as 10−12 mol/L for four kinds of cancer biomarkers, which provides a promising method for the construction of highly sensitive and high-throughput SERS detection chip and the application of in vitro diagnosis.

Ti3C2Tx, as a novel two-dimensional material, displays promising prospects in NH3 detection at room temperature. However, the NH3 detection limit of pristine Ti3C2Tx is still a major research concern. Therefore, it is important to explore new Ti3C2Tx-based nanocomposites for better NH3-sensing performance. In the present experiment, Ti3C2Tx/In2O3 nanocomposites were successfully synthesized by ultrasonication and characterized by XRD, FESEM, TEM, XPS, and BET. The optimal Ti3C2Tx/In2O3-based sensor had a high response of 63.8% (30.4 times higher than that of pristine Ti3C2Tx) to 30 ppm NH3 at room temperature. In addition, the optimal Ti3C2Tx/In2O3-based sensor had stable repeatability, excellent selectivity, and long-term stability, while exhibiting excellent potential for NH3 detection at room temperature.

Benzoyl peroxide (BPO) has been added in wheat flour because of its bleaching effect. However, the abnormal used BPO has caused increasing concern due to its strong oxidization capability which may have adverse effects on living organisms. Herein, we present a carbon dot (CD)-based fluorescent and colorimetric probe for visually, sensitively and selectively sensing BPO. The addition of BPO could quench the red fluorescence of CDs peaked at 622 and 677 nm, and decrease the absorbance at 613 nm, while increase the absorbance at 450 nm, resulting in a fluorescence turn-off and colorimetric spectral response. Moreover, the CDs had short response time of 10 min and high sensitivity towards BPO with a low limit of detection of 28 nmol/L. The applicability of the CDs in detecting BPO in wheat, noodle and starch samples was further demonstrated, and good recovery results were obtained.

Because the widely used perfluorooctane sulfonate (PFOS) is harmful to both environment and human health, it is of great significance and urgency to develop sensitive and selective sensors for the detection of trace PFOS in water. In this study, a tetraphenylethylene-derived macrocycle BowtieCyclophane has been developed as a fluorescent sensor based on aggregation-induced emission enhancement and fluorochromism. Sensitive detection of PFOS has been achieved with a limit of detection (LOD) of 47.3 ± 2.0 nmol/L (25.4 ± 1.1 μg/L) accompanied by visual fluorescence color changes.

l -kynurenine (L-kyn) is a marker of prostate cancer. At present, the expensive instruments are usually applied to detect L-kyn in clinically, which limits its wide application for cancer diagnosis. Herein, three lanthanide metal–organic frameworks ([Ln(CHO2)3]n, Ln = Eu, Gd, and Tb) were designed and obtained, and detailly characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and luminescence spectroscopy. Further study reveals that [Tb(CHO2)3]n is a highly selective, ultra-sensitive, of strong anti-interference, highly stable, and non-expensive sensor for prostate cancer marker L-kyn. The limit of detection (LOD) for L-kyn sensing is a highly sensitive value of 1.0 × 10−9 mol/L. Furthermore, the sensing mechanism is discussed in detail.

An electrochemical sensor (carboxylatopillar[5]arene-coated nitrogen-doped carbon dots, namely CCDs) based on carboxylatopillar[5]arene (CP[5]) functionalized nitrogen-doped carbon dots (N-CDs) has been developed in a facile and economic manner. To improve the performance of this electrochemical sensor in pesticide detection, the optimal solution pH (pH 7) and loading amount of CCDs on the electrode (0.50 mg/mL) have been determined. By virtue of the good conductivity of N-CDs and the molecular recognition property of CP[5], CCDs modified glassy carbon electrode, namely CCDs/GCE, shows excellent anti-interference capability, selectivity, stability, and reproducibility in the sensitive detection of paraquat. The peak currents are proportional to the paraquat concentration (from 0.1 µmol/L to 10 µmol/L) with a detection limit of 6.4 nmol/L (S/N = 3), indicating a great potential in pesticide detection. In comparison with the electrochemical sensors that require expensive metal nanoparticles and complex preparation processes, CCDs/GCE exhibits excellent detection capability of paraquat with lower cost and simpler preparation processes.

Magnetic particles (MPs) are the most widely used commercialized engineering particles, which gained great success in various biological applications. Inspired by their intrinsic Fe isotope composition, we discovered a commercialized MPs-internal standard's novel function to realize the accurate quantification of biomolecules. The bioassay of carcinoembryonic antigen (CEA) was chosen as a modal system. The Fe isotope in MPs and Au isotope in report probes were simultaneously and sensitively detected by the elemental mass spectrometry. 197Au/57Fe isotopic ratios and CEA concentrations showed good linearity in the range of 0.6–300 ng/mL, with a detection limit of 0.09 ng/mL (3σ). The accuracy and precision of the proposed MPs-based immunoassay were greatly improved, by eliminating potential MPs loss during magnetic separation and absolute intensity fluctuations. Considering the exceptional availability and universality of commercialized MPs, the proposed method might open a new avenue for MPs' biological applications.

Colorimetric biosensors, based on enzyme-like nanomaterials, have come into the spotlight in virtue of their visual detection. Herein, a daisy-like zeolitic imidazolate framework-67/reduced grapheme oxide (ZIF-67/rGO) nanozyme with unique 3D hierarchical structures has been designed to realize visual detection of hydrogen peroxide (H2O2) that is recognized as a strong oxidizing agent or reactive oxygen species associated with oxidative stress in biological systems. The daisy-like ZIF-67/rGO is prepared by a facile one-step liquid-phase method conducted under room temperature. The successful introduction of rGO endows the daisy-like ZIF-67/rGO nanozyme with abundant porous structure, high specific surface area, and good charge transfer capability, which significantly accelerates the adsorbability and recognition towards the substrates and the oxidation rate of TMB-H2O2 reaction, and thus improving the nanozyme activity observably. It is conductive to nanozyme-modulated H2O2 determination. The established colorimetric biosensor platform based on ZIF-67/rGO nanozyme exhibits remarkable sensitivity and high specificity for the application in visual detection of H2O2. The detection limit of ZIF-67/rGO-based biosensor platform is as low as 3.81 μM, which is nearly 8 times lower than that of ZIF-67-based biosensor platform. Moreover, its potential applicability as an ideal platform for colorimetric biosensors is demonstrated by testing the concentration of H2O2 in milk samples, which sheds light on the promising application of the proposed biosensing system in point-of-care detection.

As one of the specific biomarkers of anthrax, timely, sensitive and accurate detection of 2,6-dipicolinic acid (DPA) plays an important role in preventing biological weapons attacks and disease outbreaks. Here, multiemission Eu3+/covalent- organic framework (COFDTA-TFP) and Tb3+/COFDTA-TFP were constructed by the coordination between Eu3+ or Tb3+ with fluorescent COFDTA-TFP which was prepared by amine-aldehyde dehydration condensation between 2,5-diaminoterephthalic acid and 2,4,6-triformylphloroglucinol for the first time. The Eu3+/COFDTA-TFP and Tb3+/COFDTA-TFP can emit non-overlapping fluorescence of COFDTA-TFP and Eu3+ or Tb3+, which was used to ratiometric detection of DPA. Due to the strong coordination between the nitrogen atoms in the pyridine ring and the oxygen atoms in the carboxyl group of DPA with Eu3+ or Tb3+, DPA replaced coordinated H2O to sensitize fluorescence of Eu3+ or Tb3+ by “antenna” effect but fluorescence of COFDTA-TFP with two-dimensional lamellar structure was kept constant as a reference. The linear range and detection limit of ratiometric fluorescence sensor based on Eu3+/COFDTA-TFP for detection of DPA are 0.01–12 µM and 4.2 nM, respectively. The linear range and detection limit of ratiometric fluorescence sensor based on Tb3+/COFDTA-TFP for detection of DPA are 0.01–9.0 µM and 2.9 nM, respectively.

Cysteine, an organic small molecule containing a sulfhydryl group, plays key roles in human physiology and disease. The detection of cysteine in vitro and in vivo is essential for further elucidating its many biological functions. Herein, we designed and synthesized a coumarin-based fluorescent probe for cysteine detection. This probe was successfully applied to the monitoring of cysteine in living HeLa cells, indicating that this probe can penetrate viable cell membranes and selectively detect cysteine in the presence of other analytes such as homocysteine and glutathione. The linear relationship of Cys in the range of 0-50 µM and the limit of detection (LOD) of the probe 1 was 1.3 μM, provides a potential possibility for the quantitative study of intracellular Cys.

A highly sensitive electrochemical sensor was developed through a one-pot green synthesis method for nitrite detection based on the electrochemical technique. Xylan-based carbon quantum dots (CQDs) were used as green in situ reducing agent to prepare CQDs capped gold nanoparticles (Au@CQDs). MXene of good electrical conductivity was used as the immobilized matrix to fabricate Au@CQDs-MXene nanocomposites with the advantages of good electrical conductivity and electrocatalysis. An electrochemical sensor for nitrite monitor was obtained by loading the Au@CQDs-MXene on a glassy carbon electrode. The sensor presents high sensitivity, good stability, wide linear range, and excellent selectivity due to the high catalytic activity of AuNPs and CQDs, the large specific surface area of MXene, and exceptional electrical conductivity of AuNPs and MXene. Under the optimal condition, the linear detection range of the sensor was from 1 μM to 3200 μM with a detection limit of 0.078 μM (S/N = 3), which was superior to most reported sensors using differential pulse voltammetry (DPV) method. Furthermore, this sensor was successfully applied to detect nitrite in tap water and salted vegetables with satisfactory recoveries. This modified electrocatalytic sensor shows a new pathway to fabricate nitrite detection sensor with feasibility for practical application.

Photoelectrochemical (PEC) sensor is an emerging technology in analysis as the advantage of fast response, high sensitivity and uncomplicated operation. In this study, an effective label-free PEC sensor for bisphenol A (BPA) detecting is constructed, in which ZnIn2S4/g-C3N4 heterojunction is prepared via a simple hydrothermal method. The characterization outcomes display that the formation of p-n heterojunction helps for promoting the separation efficiency of photo-generated carrier. Under visible light irradiation, the ZnIn2S4/g-C3N4 modified electrode exhibits broader liner range from 0.05 mmol/L to 30 mmol/L and lower detection limit of 0.016 μmol/L (S/N=3) with remarkable stability and reproducibility of detection BPA under visible light irradiation. Furthermore, the constructed PEC sensor displays favorable potential for detection of BPA in practical applications.

The metal oxides-based chemiresitive gas sensors have attracted enormous interest because of their exellent sensing perforamcnes, which have emerged as very promising candidates for gas monitoring. However, from the view of organophosphorus compounds detection, a unique combination of low detection limit and fast respons/recovery rate remains challenging. Herein, the synersgitic effects of oxygen vacancy engineering and surface gold decoration enabling excellent sensing performances for detection of dimethyl methyl phosphonate (DMMP, a typical organophosphorus) is reported. To demonstrate the proof of concept, Au nanoparticles (NPs) decorated oxygen vacancy-enriched SnO2 hybrids (designated as Au-O-SnO2) were designed as sensing materials, where the O-SnO2 samples were fabricated by introduction of oxygen vacancies onto commercial SnO2 through organometallic chemistry-assisted approach using (CH3)2SnCl2 as precursor, followed by deposition of Au NPs by an in-situ reduction routine. After optimizing Au NPs content in hybrids (1 wt%, 3 wt%, 5 wt% and 7 wt%), O-SnO2 decorated with 5 wt% Au NPs (designated as Au-O-SnO2-5) exhibits excellent DMMP sensing performances, such as, an enhanced recoverable response of 1.67 to 680 ppb DMMP, low detection limit of 4.8 ppb, short response time of 26 s and recovery time of 32 s, as well as good selectivity, which are much better than that of commercial SnO2 (C-SnO2) and O-SnO2, and Au NPs decorated C-SnO2. Based on the detailed investigation, the enhanced DMMP sensing performances of Au-O-SnO2 hybrids can be mainly ascribed to the synergistic effect of increasing surface active sites induced by oxygen vacancies, the chemical and electronic sensitization of Au NPs. As a result, Au-O-SnO2-5 hybrids display relatively low activation energy of 24.11 kJ/mol for DMMP oxidization, which is lower than that of O-SnO2 (35.54 kJ/mol). Our results provide a feasible method for boosting sensing performances for DMMP detection, paving new way for fabrication of metal oxides-based gas sensors for rapid detection of trace organic compounds with complexed structures.

Tetracycline (TET) is one of the common antibiotics used in animal husbandry. However, the long-term consumption of TET may increase the risks for human health, especial in dairy products. Moreover, after entering the human body, TET is difficult to be absorbed by the intestines and stomach, and will be discharged into the sewage in the form of the parent compound, which will cause irreversible damage to the natural environment. Novel nitrogen-doped carbon dots (N-CDs) nanoparticles were successfully fabricated using in situ hydrothermal reaction on the inner surface of the aminated central radial silica spheres (CRSSs-NH2), called CRSSs-NH2@N-CDs. The aminated central radial carrier played a role in protecting and stabilizing N-CDs, thus enhancing it fluorescence and realizing solid-state light emission. The results shown that the optimal excitation wavelength of CRSSs-NH2@N-CDs was about 365 nm, and the emission wavelength was about 446 nm. The CRSSs-NH2@N-CDs was then used as a fluorescent probe for rapidly detecting TET. With optimized experimental conditions, the fluorescence quenching intensity of CRSSs-NH2@N-CDs had a good linear relationship with the concentration of TET. The linear detection range was 0.5–60 μM, and the limit of detection is 0.39 μM. Furthermore, the TET-sensing application in milk has been carried out, and the average recovery range is 91.90%–104.70%.

Bladder cancer is the most common malignant tumours with high morbidity, mortality and recurrence. However, currently developed detection methods for bladder cancer-associated urine biomarkers are hindered by their extremely low abundance. Hence, the exploration of a highly sensitive and selective approach for the detection of trace bladder cancer-associated biomarkers in human urine is of vital importance for the diagnosis of bladder cancer. Herein, we developed a highly reliable indium gallium zinc oxide field effect transistor (IGZO FET) biosensor for the detection of bladder cancer-related biomarker microRNA. The single-stranded DNA-functionalized IGZO FET biosensors exhibit high sensing reproducibility and stability with an ultralow detection limit of 19.8 amol/L. The device could also be used for quantitative detection of trace microRNA in human urine samples and can effectively distinguish bladder cancer patients from healthy donors. The development of high performance IGZO FET biosensors presents new opportunities for the achievement of early-stage diagnosis of bladder cancer.

Surface plasmon resonance (SPR) technology has become one of the powerful tools for real-time bioassay of various targets without needing labels. However, SPR biosensing faces great challenge with the extension of application fields due to the limited sensitivity. Herein, we report an ultrasensitive SPR biosensing strategy for detecting carcinoembryonic antigen (CEA) with the introduction of amino-functionalized Ti3C2-MXene (N-Ti3C2-MXene) nanosheets. The ultrathin Ti3C2-MXene nanosheets were prepared by hydrochloric acid (HF) etching and further modified by (3-aminopropyl) triethoxysilane (APTES) to obtain amino terminals for conjugating polyclonal anti-CEA antibody (Ab2) via covalent bonding. Staphylococcal protein A (SPA) decorated Au film was utilized as sensing platform to orientedly immobilize monoclonal anti-CEA antibody (Ab1) via its Fc region. The N-Ti3C2-MXene-Ab2 nanoconjugates were introduced to the sensing system after capture of CEA, forming sandwiched immunocomplexes on the SPR chip. A signal amplification strategy of Ti3C2-MXene-induced spontaneous gold reductive deposition on Ti3C2-MXene nanosheets was employed to further enhance sensitivity. The proposed biosensor exhibits a wide linear range for CEA determination of 10−11 to 10−6 g mL−1 with a detection limit of 1.7 pg mL−1 (S/N=3). Moreover, good reproducibility and high specificity were demonstrated by serum samples analysis, which indicates the present method holds potential in evaluating CEA in human serum for early diagnosis and monitoring of cancer.

Riboflavin (RF) is one of the necessary vitamins. If human body lacks RF, it will lead to inflammation and dysfunction of mouth, lips and skin. Thus sensitive and accurate determination of RF is necessary. Here, an electroactive covalent-organic framework nanobelt (COFTFPB-Thi) with thickness of 1.4 nm was prepared by amine-aldehyde condensation reaction between thionine and 1, 3, 5-tris (p-formylphenyl) benzene, which was then grown vertically on three-dimensional porous carbon derived from kenaf stem (3D-KSC) for double signal ratiometric electrochemical detection of RF. The resulted 3D-KSC/COFTFPB-Thi showed two reduction peaks at −0.08 V and −0.23 V, which came from the reduction of COFTFPB-Thi and the conjugated structure of COFTFPB-Thi, respectively. In the presence of RF, those RF molecules near the electrode surface were oxidized at 0.6 V. Then some oxidized RF (RFox) adsorbed on COFTFPB-Thi would oxidize COFTFPB-Thi into COFTFPB-Thi(ox) while other RFox adsorbed on 3D-KSC kept unchanged. When the potential was scanned from 0.6 V to −0.6 V, both COFTFPB-Thi(ox) and RFox adsorbed on 3D-KSC were reduced at −0.08 V and −0.45 V accordingly, while the reduction peak of −0.23 V of the conjugated structure of COFTFPB-Thi kept constant. When j-0.45/j-0.23 was used as the response signal, the detection limit was 44 nM and the linear range was 0.13 μM −0.23 mM. By using j-0.08/j-0.23 as the response signal, a detection limit of 90 nM and a linear range of 0.30 μM-0.23 mM (S/N = 3) were obtained. By using double signals, the measurement results can be corrected to make the results more accurate and reliable. The sensor also showed good selectivity, reproducibility and stability, which provided a good application prospects.

A reliable and sensitive strategy which can assess nucleic acid levels in living cells would be essential for fundamental research of biomedical applications. Some nanomaterial-based fluorescence biosensors recently developed for detecting nucleic acids, however, are often with expensive, complicated and time-consuming preparation process. Here, by using a facile bottom-up synthesis method, a two-dimensional (2D) coordination polymer (CP) nanosheet, [Cu(tz)] (Htz = 1,2,4-triazole), was successfully prepared after optimizing reaction conditions. These ultrathin CP nanosheets with thickness of 4.7 ± 1.1 nm could readily form nanosensors by assembly with DNA probes, which exhibited a low limit of detection (LOD) for p53 DNA fragment as 144 pmol/L. Furthermore, by integrating [Cu(tz)] nanosheets with hybridization chain reaction (HCR) probes, miR-21, one kind of microRNA upregulated in many cancer cells, can be sensitively detected with a LOD of 100 pmol/L and monitored in living cells, giving consistent results with those obtained by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis. Thus [Cu(tz)] nanosheets, which not only possess much better nucleic acids sensing performance than bulk cystals, but also exhibit nucleic acid delivery functions, could be used as a novel nanoplatform in biomedical imaging and sensing applications.

A fluorescent carbon quantum dots(N-S CQDs) doped with nitrogen, and sulfur with tunable wavelength was successfully prepared by one-step hydrothermal reaction for sensitive detection of Pb2+. The doping of N and S narrows the band gap of the CQDs and makes the wavelength red shift, so that the carbon quantum dots displayed maximum emission peak at 540 nm under 460 nm excitation. The addition of Pb2+ quenched the fluorescence due to the specific combination of Pb2+ with the carboxyl and sulfhydryl on the surface of the CQDs formed a coordination structure. Under optimal conditions, the carbon quantum dots revealed outstanding anti-interference capability and a favorable linear relation was obtained in the scope of 0.2-12 μM and 40-200 μM with the limit of detection of 0.097 μM and 5.624 μM for Pb2+. Besides, the CQDs had been successfully used for monitoring Pb2+ in river water with well accuracy and recovery.

Chromium is a harmful contaminant showing mutagenicity and carcinogenicity. Therefore, detection of chromium requires the development of low-cost and high-sensitivity sensors. Herein, blue-fluorescent carbon quantum dots were synthesized by one-step hydrothermal method from alkali-soluble Poria cocos polysaccharide, which is green source, cheap and easy to obtain, and has no pharmacological activity due to low water solubility. These carbon quantum dots exhibit good fluorescence stability, water solubility, anti-interference and low cytotoxicity, and can be specifically combined with the detection of Cr(VI) to form a non-fluorescent complex that causes fluorescence quenching, so they can be used as a label-free nanosensor. High-sensitivity detection of Cr(VI) is achieved through internal filtering and static quenching effects. The fluorescence quenching degree of CDs fluorescent probe showed a good linear relationship with Cr(VI) concentration in the range of 1–100 μM. The linear equation was F0/F = 0.9942 + 0.01472[Cr(VI)] (R2 = 0.9922), and the detection limit can be as low as 0.25 μM (S/N = 3), which has been successfully applied to Cr(VI) detection in actual water samples herein.

Three-dimensional (3D) plasmonic nano-arrays can provide high surface-enhanced Raman scattering (SERS) sensitivity, good spectral uniformity and excellent reproducibility. However, it is still a challenge to develop a simple and efficient method for fabrication of 3D plasmonic nano-arrays with high SERS performance. Here we report a facile approach to construct ordered arrays of silver (Ag) nanoparticles-assembled spherical micro-cavities using polystyrene (PS) sphere template-assisted electrodeposition and post-growth. The electrodeposited small Ag nanoparticles grow into bigger stable nanoparticles during the post-growth process, which could significantly improve the SERS sensitivity. The Ag nanoparticles-assembled 3D micro-cavity array provides much more hotspots in the excitation laser beam-covered volume than the two-dimensional counterpart. The relative standard deviation (RSD) of 612 cm−1 peak of rhodamine 6G (R6G) was calculated to be 8%, and the RSD of the characteristic peak taken from substrates of different batches was less than 10%. The detectable lower concentration as low as 1 fM was achieved for an aqueous solution of R6G. Such SERS substrate also showed high sensitivity to thiram (fungicide) and paraquat (herbicide) in water with limits of detection of 0.067 nM and 2.5 nM respectively. Furthermore, it also demonstrated that SERS detection of pesticide residues on fruits can be realized, showing a potential application in rapid monitoring food safety.

Herein, a label-free, self-enhanced electrochemiluminescence (ECL) sensing strategy for divalent mercury (Hg(II)) detection was presented. First, a novel self-enhanced ECL luminophore was prepared by combining the ECL reagent tris(2, 2′-bipyridyl) dichlororuthenium(II) hexahydrate (Ru(bpy)32+) and its co-reactant carbon nitride quantum dots (CNQDs) via electrostatic interactions. In contrast to traditional ECL systems where the emitter and its co-reactant underwent an intermolecular reaction, the self-enhanced ECL system exhibited a shortened electron-transfer distance and enhanced luminous efficiency because the electrons transferred from CNQDs to oxidized Ru(bpy)32+ via an intramolecular pathway. Furthermore, the as-prepared self-enhanced ECL material was encapsulated in silica (SiO2) nanoparticles to generate a Ru-QDs@SiO2 luminophore. Based on the different affinity of Ru-QDs@SiO2 nanoparticles for single-stranded DNA (ssDNA) and Hg(II)-triggered double-stranded DNA (dsDNA), a label-free ECL biosensor for Hg(II) detection was developed as follows: in the absence of Hg(II), ssDNA was adsorbed on Ru-QDs@SiO2 surface via hydrogen bond, electrostatic, and hydrophobic interaction. Thus, quenched ECL signal was observed. On the contrary, in the presence of Hg(II), stable dsDNA was formed and carried the ssDNA separating from Ru-QDs@SiO2 surface, resulting in most of Ru-QDs@SiO2 existing in their free state. Therefore, a recovered ECL intensity was obtained. On this basis, Hg(II) was measured by the proposed method in the range of 0.1 nM-10 μM, with a detection limit of 33 pM. Finally, Hg(II) spiked in water samples was measured to evaluate the practicality of the fabricated biosensor.