Highly sensitive nitrite sensor based on AuNPs/RGO nanocomposites modified graphene electrochemical transistors

Room-Temperature NH3 Gas Surface Acoustic Wave (SAW) Sensors Based on Graphene/PPy Composite Films Decorated by Au Nanoparticles with ppb Detection Ability

Exhaled human breath analysis has great potential for the diagnosis of diseases in non-invasive way. The 13C-Urea breath test for the diagnosis of Helicobacter pylori infection indicates the ammonia concentration of 50-400 ppb in the breath. This work successfully developed a surface acoustic wave (SAW) resonator based on graphene/polypyrrole composite films decorated by gold nanoparticles (AuNPs-G/PPy) with sensitivity and selectivity to detect ammonia in parts-per-billion concentrations, which is promising for the accurate diagnosis of H. pylori infection. XRD, EDS, and SEM characterized the AuNPs-G/PPy nanocomposites, providing comprehensive insights into their structural, compositional, and morphological properties. The gas-sensing capabilities of the fabricated SAW sensors were extensively investigated, focusing on their response to NH3 gas at ambient temperature. The concentration of ammonia gas was effectively quantified by monitoring the frequency shift of the SAW device. Notably, our developed SAW sensor demonstrated outstanding sensitivity, selectivity, repeatability, and reproducibility for 50-1000 ppb NH3 in dry air. The excellent sensing performance of the AuNPs-G/PPy hybrid composite film can be attributed to the synergistic effects of graphene's superior conductivity, the catalytic properties of gold nanoparticles, and the conductivity sensitization facilitated by electron-hole recombination on the polypyrrole surface.

Novel graphene electrochemical transistors incorporating zirconia inorganic molecular imprinted layer：Design, construction and application for highly sensitive and selective detection of acetaminophen

Owing to their intrinsic amplifying effect together with chemical stability, graphene electrochemical transistor sensors (GECTs) are gaining momentum for sensing applications. However, the surface of GECTs for different detection substances must be modified with different recognition molecules, which was cumbersome and lack a universal method. Molecularly imprinted polymer (MIP) is a kind of polymer with specific recognition function for given molecules. Here, MIP and GECTs were combined to effectively solve the problem of weak selectivity of GECTs, and achieve the high sensitivity and selectivity of MIP-GECTs equipment in detecting acetaminophen (AP) in complex urine environment. A novel molecular imprinting sensor based on Au nanoparticles modified zirconia (ZrO₂) inorganic molecular imprinting membrane on reduced graphene oxide (ZrO₂-MIP-Au/rGO) was proposed. ZrO₂-MIP-Au/rGO was synthesized by one-step electropolymerization using AP as template, ZrO₂ precursor as the functional monomer. The -OH group on ZrO₂ and the -OH/-CONH- group on AP were easily bonded by hydrogen bonding to form a MIP layer on the surface, which allows the sensor to have a large number of imprinted cavities for AP specific adsorption. As a proof of method, the GECTs based on ZrO₂-MIP-Au/rGO functional gate electrode has the characteristics of wide linear range (0.1 nM-4 mM), low detection limit (0.1 nM) and high selectivity for AP detection. These achievements highlight the introduction of specific and selective MIP to GECTs with unique amplification function, which could effectively solve the problem of selectivity of GECTs in complex environments, suggesting the potential of MIP-GECTs in real-time diagnosis.

Electrochemical Behavior of β-Cyclodextrin-Ni-MOF-74/Reduced Graphene Oxide Sensors for the Ultrasensitive Detection of Rutin

Rutin, as a biological flavonoid glycoside, has very important medicinal value. The accurate and rapid detection of rutin is of great significance. Herein, an ultrasensitive electrochemical rutin sensor based on β-cyclodextrin metal-organic framework/reduced graphene oxide (β-CD-Ni-MOF-74/rGO) was constructed. The obtained β-CD-Ni-MOF-74 was characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption and desorption. The β-CD-Ni-MOF-74/rGO presented good electrochemical properties benefiting from the large specific surface area and good adsorption enrichment effect of β-CD-Ni-MOF-74 and the good conductivity of rGO. Under optimal conditions for the detection of rutin, the β-CD-Ni-MOF-74/rGO/GCE showed a wider linear range (0.06-1.0 μM) and lower detection limit (LOD, 0.68 nM, (S/N = 3)). Furthermore, the sensor shows good accuracy and stability for the detection of rutin in actual samples.

Graphene electrochemical transistors decorated by Ag nanoparticles exhibiting high sensitivity for the detection of paraquat over a wide concentration range

Paraquat (PQ) is a nonselective contact herbicide used in agriculture for the control of broad leaf weeds, which would cause irreversible damage to human organs even at very low concentrations. Therefore, the trace residue detection of PQ in the environment is of vital importance. Here, a novel graphene electrochemical transistor (GECT) for PQ detection is reported for the first time. The key to the device design is the application of a layer of Ag nanoparticle (Ag NP) modified monolayer graphene as the channel layer. Due to the good electrochemical activity of Ag NPs for PQ detection, the device exhibits excellent sensitivity for PQ with the detection limit of 0.068 nM and a wide linear range from 0.1 nM to 5 mM. The GECT sensor also reveals good selectivity toward several common interferents and exhibits satisfactory recoveries for PQ detection when using Chinese cabbage as a simulant to deduce the real detection situation. The GECT sensor not only provides an efficient method for the detection of PQ residues, but also provides an effective grafting platform for the construction of novel high-sensitivity electrochemical sensors.

Graphene electrochemical transistor incorporated with gel electrolyte for wearable and non-invasive glucose monitoring

With the rapid development of wearable electronic devices, health monitoring is undergoing a fundamental shift from hospital-centered treatment to patient-centered diagnosis. Solution-gated graphene transistors provide an effective platform for developing high-sensitivity wearable devices due to their unique signal amplification, low energy consumption, and compatibility for miniaturization. However, it is still a major challenge to perform real-time sweat composition monitoring directly on the dry skin surface. In this work, a skin-based flexible gel electrolyte graphene transistor (GEGT) was successfully designed and fabricated for glucose detection, consisting of a gate electrode decorated with Au nanoparticles modified reduced graphene oxide (AuNPs/RGO) nanocomposites and a monolayer graphene channel. Glycerin gel was used to replace the traditional liquid electrolyte, not only could better fit the human skin, but also play the role of fluid collection, providing stable testing conditions for the sensor. Based on the high electron mobility of graphene channel and the excellent electrocatalytic performance of AuNPs/RGO nanocomposites, the constructed GEGT sensor exhibits excellent sensing performance for glucose with good selectivity, low operating voltage (0.5 V), wide detection range (10 nM - 25 mM), and low detection limit (10 nM). The device maintains stable performance after up to 1000 bending cycles with a bending radius of 4 mm. In addition, the GEGT sensor displays good accuracy in sweat detection and sensitive dynamic response during actual wearing, which provides a guarantee for the construction of wearable transistor devices and real-time health tracking.

Recent Advances in Biosensor Technologies for Point-of-Care Urinalysis

Human urine samples are non-invasive, readily available, and contain several components that can provide useful indicators of the health status of patients. Hence, urine is a desirable and important template to aid in the diagnosis of common clinical conditions. Conventional methods such as dipstick tests, urine culture, and urine microscopy are commonly used for urinalysis. Among them, the dipstick test is undoubtedly the most popular owing to its ease of use, low cost, and quick response. Despite these advantages, the dipstick test has limitations in terms of sensitivity, selectivity, reusability, and quantitative evaluation of diseases. Various biosensor technologies give it the potential for being developed into point-of-care (POC) applications by overcoming these limitations of the dipstick test. Here, we present a review of the biosensor technologies available to identify urine-based biomarkers that are typically detected by the dipstick test and discuss the present limitations and challenges that future development for their translation into POC applications for urinalysis.

Lignosulfonate in situ-modified reduced graphene oxide biosensors for the electrochemical detection of dopamine

Lignosulfonate (LS), a biomass by-product from sulfite pulping and the paper-making industry, which has many excellent characteristics, such as renewable, environmentally friendly, amphiphilic nature, and especially the abundant content of hydrophilic functional groups in its architecture, making it highly reactive and can be used as a sensitive material in sensors to show changes in electrical signals. Herein, we report a one-step in situ method to fabricate lignosulfonate-modified reduced graphene oxide (LS-rGO) green biosensors, which can be used for the sensitive electrochemical detection of dopamine without interference from uric acid and ascorbic acid. The modified LS molecular layers act as chemical-sensing layers, while the rGO planar sheets function as electric-transmitting layers in the as-assembled dopamine biosensors. After the in situ-decoration of the LS modifier, the sensing performance of LS-rGO for the detection of dopamine was much higher than that of the pure rGO electrode, and the highest current response of the biosensor toward dopamine greatly improved from 11.2 μA to 52.07 μA. The electrochemical sensitivity of the modified biosensor was optimized to be 0.43 μA μM^-1, and the detection limit was as low as 0.035 μM with a wide linear range (0.12-100 μM), which is better than that of most previously reported metal- and organic-based modified graphene electrodes. The newly designed biosensor has unique advantages including rapid, stable, sensitive and selective detection of dopamine without interference, providing a facile pathway for the synthesis of green resource-derived sensing materials instead of the traditional toxic and expensive modifiers.

Gold Nanomaterials and their Composites as Electrochemical Sensing Platforms for Nitrite Detection

Nitrite is one of the abundant toxic components existing in the environment and is likely to have a great potential to affect human health badly. For that reason, it has become crucial to build a reliable nitrite detection method. In recent years, several nitrite monitoring systems have been proposed. Compared with traditional analytical strategies, the electrochemical approach has a bunch of advantages, including low cost, rapid response, easy operation, simplicity, etc. In this case, noble metal nanomaterials, especially Au-based nanomaterials, have attracted attention in electrode modification because of higher catalytic activity, facile mass transfer, and broad active area for determining nitrite. This review is based on the state-of-the-art, which includes a variety of nanomaterials that have been coupled with AuNPs for the creation of nanocomposites, and the construction as well as development of electrochemical sensors for nitrite detection over the last few years (2016-2022). A background study on synthesizing different morphological AuNPs and nanocomposites has also been introduced. The fabrication methods and sensing capabilities of modified electrodes are given special consideration.

Rapid detection of nitrite based on nitrite-oxidizing bacteria biosensor and its application in surface water monitoring

Timely and sensitive detection of nitrite is of great significance for human health protection and water pollution treatment. However, many biosensors can only determine the comprehensive toxicity of the water, and there are few electroactive biofilm (EAB) sensors for the specific detection of pollutants. Biofilms formed by bacteria with specific functions can improve the specificity of nitrite identification by biosensors. This study developed a novel, rapidly responding, high sensitivity (958.6 μAμM^-1cm^-2), wide detection range and anti-interference electrochemical biosensor based on electroactive nitrite-oxidizing bacteria. The biosensor could accurately detect nitrite in the range of 0.3-100 mg/L within 3 min by the cyclic voltammetry (CV) method. The bioelectrode could perform stable detection of nitrite over 200 cycles. The specificity of the biosensor for detecting nitrite was demonstrated by the presence of nitrite oxidizing bacteria (NOB) and nitrite oxidase enzyme (NXR) on the electrode biofilm. The biosensor performed well in wetlands and rivers, with an RSD <14.8% in the detection of nitrite at low concentrations, and further revealed the nitrification occurrence. Our study provided a feasible way for the development of a highly sensitive, rapidly responding and stable electrochemical biosensor, which also exhibited potential applications for long-term detection of nitrite and assessment of ecological function in surface water (rivers, lakes, wetlands, marshes, etc.).

A novel electrochemical sensor based on nitrite-oxidizing bacteria for highly specific and sensitive detection of nitrites

Real-time nitrite control in water is necessary for environmental safety and human health, and has triggered the research and development of novel detection methods. Previous studies have made great progress on enzyme-free and enzyme electrochemical sensors. However, enzyme-free sensors have low selectivity and a complex preparation process, and enzyme sensors have short lifetimes, and these issues need to be addressed. In this work, we proposed for the first time a highly specific and sensitive biofilm sensor based on nitrite-oxidizing bacteria (NOB) for the bio-electrochemical detection of nitrite in water. The mechanism of nitrite detection was attributed to the competition of oxygen between aerobic respiration of the NOB and the cathode oxygen reduction on the carbon felt electrode, resulting in a decrease in current. This decrease in current (ΔI) had a linear relationship with the nitrite concentration in the range of 0.1 to 1 mg L^-1 and 1 to 10 mg L^-1, which was corresponding to the sensitivities of 48.62 and 2.24 μA mM^-1 cm^-2, respectively. And the limit of detection (LOD) was calculated to be 0.033 mg L^-1 (2.39 μM) with a signal-to-noise ratio of 3. Moreover, several common interfering ions had no effect on the nitrite detection owing to the functional microbial species (NOB) and weakly electrochemical behavior of electrode at the low potential of -0.1 V, showing high specificity for nitrite detection of biofilm sensor. Therefore, the actual nitrified wastewater was well detected by the biofilm sensor. In addition, allylthiourea (ATU) took good effect on the resistance of the influence of ammonia oxidizing bacteria (AOB) in the biofilm sensor, maintaining the high selectivity of biofilm sensor in case the biofilm sensor was fouled with AOB. The biofilm sensor in our work showed good selectivity, sensitivity and stability in long-term detection.

Au-PEDOT/rGO nanocomposites functionalized graphene electrochemical transistor for ultra-sensitive detection of acetaminophen in human urine

A novel graphene electrochemical transistor (GECT) sensor based on Au-poly(3,4-ethylenedioxythiophene)/reduced graphene oxide (Au-PEDOT/rGO) nanocomposites functionalized the gate electrode and monolayer graphene as channel was proposed and constructed for the ultra-sensitive detection of acetaminophen (AP). Au-PEDOT/rGO nanocomposites were synthesized by a simple one-pot method to modify the gate electrode of GECT. With the high catalytic activity of Au nanoparticles, the good conductivity and stability of PEDOT, the large specific surface area and abundant adhesion sites of rGO, the sensitivity and stability of the device for AP detection could be effectively improved. The sensing mechanism of the device was that the electrochemical reactions of the AP on the surface of gate electrode causes the effective gate voltage on the GECT to change, thereby adjusting the carrier concentration and current of the graphene channel. Combined with the excellent catalytic properties of Au-PEDOT/rGO nanocomposites and the high carrier mobility of the graphene channel, the resulting device has remarkable sensing performance for AP, with a detection limit as low as 1 nM and a linear range from 1 nM to 8 mM. In addition, the device has good anti-interference ability and accuracy in the detection of AP in urine samples and tablets, which proved that it could be used to determine AP in human non-invasive and pharmaceutical products. The GECT sensor based on Au-PEDOT/rGO provides an efficient, sensitive and cost-effective sensing platform for AP detection, and is expected to realize in vitro diagnosis of diseases.

Nanoglycocluster based diagnostic platform for colorimetric detection of bacteria; A comparative study analysing the effect of AuNPs size, linker length, and glycan diversity

Nanoglycoclusters, an upcoming class of functional nanomaterial are known to drive various processes like detection, imaging, targeting proteins, cells, and bacteria. Nanoglycoclusters are a type of nanomaterial functionalized with various glycans. The array of glycan in multiple copies enhances binding affinity with proteins. Selective and sensitive bacteria/lectin interactions using nanomaterials are an emerging area of research. The measurement of different ligand receptor interactions require sophisticated analytical tools that limit the application in biosensor domain. Recently, colorimetric biosensors gained importance in the field of the biosensor for the detection of bacteria/lectins. Herein we have demonstrated that different size of gold nanoparticles (AuNPs) along with various polyethylene glycol (PEG) linkers, functionalized with synthesized monopod and tripod of mannose and galactose that have different bacteria/lectins specificity. The newly synthesized nanoglycoclusters were able to discriminate between different lectins and bacteria. The aggregation of specific nanoglycocluster upon interaction with specific bacteria/lectins revealed that mannose monopod (MM) and mannose tripod (MT) are specific to Escherichia coli and concanavalin A (ConA) lectin, while galactose monopod (GM) and galactose tripod (GT) are specific to Pseudomonas aeruginosa and Peanut agglutinin (PNA) lectin. Further, the binding events depict the affinity of tripod glycans is more with respect to its corresponding monopod glycans. Our findings explored the potential of colorimetric sensing depending upon the size of AuNPs, linker length, specificity, along with glycans density to develop user friendly diagnostic system for the detection of bacteria.

A sensitive electrochemical sensor based on metal cobalt wrapped conducting polymer polypyrrole nanocone arrays for the assay of nitrite

The conducting polymer polypyrrole nanocones wrapped by metal cobalt (Co/PPy) are a promising platform for the detection of sodium nitrite, which can be obtained by an electrochemical deposition technique under a mild condition. Co/PPy nanocone arrays combined the high conductivity and large specific surface area of PPy nanocones with the redox properties of metal cobalt, and their 3D structure can provide more active sites for nitrite detection. Owing to the microstructure and excellent electrical properties of the nanocomposite, Co/PPy nanocone arrays were convenient to construct a high-performance nitrite sensor. The microscopic morphology and composition of Co/PPy nanocone arrays were characterized by SEM, FT-IR, XPS, and XRD, and their electrochemical performances were also investigated. The experimental results showed that Co/PPy nanocones exhibited excellent performance for nitrite determination. The sensors were used for the determination of nitrite in pickled Chinese cabbage and water samples, and the results were consistent with those of spectrophotometry. Hence, the synthesized Co/PPy nanocone arrays have a broad application prospect in food safety, environmental protection, and industrial manufacturing.

Materials Approaches for Improving Electrochemical Sensor Performance

Electrochemical sensors have emerged as important diagnostic tools in recent years, due to their simplicity and ease of use. Compared to instrumental analysis methods that use complicated experimental and data analysis techniques─such as mass spectrometry, nuclear magnetic resonance (NMR), spectrophotometric methods, and chromatography─electrochemical sensors show promise for use in a wide range of real-time and in situ applications such as pharmaceutical testing, environmental monitoring, and medical diagnostics. In order to identify analytes in complex and/or biological samples, materials used for both the electrode materials and the chemically selective layer have been evolving throughout the years for optimizing the analytical performance of electrochemical sensors to increase sensitivity, selectivity and linear range. In this Perspective, attention will be focused on different types of materials that have been used for electrochemical sensing, including new combinations of well-studied materials as well as novel strategies to enhance the performance of sensing devices. The Perspective will also discuss existing challenges in the field and future strategies for addressing those challenges.

[Determination of nine N-nitrosamines in animal derived foods by QuEChERS-isotope dilution combined with gas chromatography-tandem mass spectrometry]

建立了同时测定动物源性食品中9种N-亚硝胺类化合物的气相色谱-串联质谱分析方法。当下动物源性食品中N-亚硝胺类化合物污染种类较多,对人体危害较大,但国标GB 5009.26-2016仅针对N-二甲基亚硝胺的检测,且存在样品前处理复杂、标准方法回收率低、再现性差等问题,因此建立同时快速检测多种N-亚硝胺类化合物的方法有一定现实意义。称取10.0 g样品,置于50 mL离心管中,加入200 μL内标工作液和10 mL乙腈,冷冻30 min后,加入4 g硫酸镁和1 g氯化钠进行脱水,以9000 r/min离心5 min。取5 mL上清液使用150 mg聚苯乙烯二乙烯苯(PLS-A)粉末净化,再使用1.6 g MgSO₄和0.4 g NaCl脱水,过0.22 μm滤膜,上机分析。在初始温度为50 ℃时采用程序升温模式,0.16 min后,以900 ℃/min的速率将温度升至220 ℃。采用毛细管气相色谱柱HP-Innowax(30 m×0.25 mm×0.25 μm)分离,使用电子轰击电离(EI)源检测,在多反应监测模式下,以保留时间和特征离子对信息进行定性和定量分析,使用内标法定量N-亚硝胺类化合物。结果表明,N-亚硝胺类化合物在0.1~50.0 μg/L范围内具有良好的线性关系,方法的检出限(S/N=3)和定量限(S/N=10)分别为0.03~0.30 μg/kg和0.10~1.00 μg/kg。对不同样品基质进行0.5、1.0、3.0 μg/kg3个水平的加标回收试验,9种N-亚硝胺类化合物的回收率为80.4%~98.5%, RSD(n=6)为2.41%~12.50%。应用建立的方法检测市面上常见的动物源性食品,除N-亚硝基乙胺、N-亚硝基吗啡胆碱外,其他7种N-亚硝胺类化合物均有不同程度检出。检测结果表明,腌制水产品中N-亚硝胺类化合物含量普遍高于其他样品。研究建立的方法操作简单,不需要长时间蒸馏提取,可快速对动物源性食品中N-亚硝胺类化合物进行定性和定量分析,且样品和试剂的消耗量更少,节省成本,对环境污染小。该法的建立对我国动物源性食品中N-亚硝胺类化合物残留水平的控制、检测标准的制定和采取相应的管理措施具有一定的理论和现实意义。

A Simple and Rapid Spectrophotometric Method for Nitrite Detection in Small Sample Volumes

A simple, rapid, and environmentally-friendly spectrophotometric method for nitrite detection was developed. Detection was based on a redox reaction with iodide ions in an acidic condition. The reaction was evaluated by detecting the increase in absorbance of the colored product of iodine at 362 nm wavelength. To obtain a good spectrophotometric performance, the iodide ions concentration, hydrochloric acid concentration, and reaction time were optimized. In the optimal condition, the developed spectrophotometric method provided a linear range of 0.0625 to 4.00 mg L−1 (r = 0.9985), reaction time for 10 min, a limit of detection of 25 µg L−1, and a limit of quantitation of 85 µg L−1. This method showed good repeatability (RSD < 9.21%), high sample throughput (9 samples min−1), and good accuracy (recovery = 88 ± 2 to 99.5 ± 0.4%). The method has the potential to be used in crime scene investigations as a rapid screening test for gunshot residue detection via nitrite detection.

Nanocomposite Materials Based on Electrochemically Synthesized Graphene Polymers: Molecular Architecture Strategies for Sensor Applications

The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors.

Graphene, an Interesting Nanocarbon Allotrope for Biosensing Applications: Advances, Insights, and Prospects

Graphene, a relatively new two-dimensional (2D) nanomaterial, possesses unique structure (e.g. lighter, harder, and more flexible than steel) and tunable physicochemical (e.g. electronical, optical) properties with potentially wide eco-friendly and cost-effective usage in biosensing. Furthermore, graphene-related nanomaterials (e.g. graphene oxide, doped graphene, carbon nanotubes) have inculcated tremendous interest among scientists and industrials for the development of innovative biosensing platforms, such as arrays, sequencers and other nanooptical/biophotonic sensing systems (e.g. FET, FRET, CRET, GERS). Indeed, combinatorial functionalization approaches are constantly improving the overall properties of graphene, such as its sensitivity, stability, specificity, selectivity, and response for potential bioanalytical applications. These include real-time multiplex detection, tracking, qualitative, and quantitative characterization of molecules (i.e. analytes [H₂O₂, urea, nitrite, ATP or NADH]; ions [Hg²⁺, Pb²⁺, or Cu²⁺]; biomolecules (DNA, iRNA, peptides, proteins, vitamins or glucose; disease biomarkers such as genetic alterations in BRCA1, p53) and cells (cancer cells, stem cells, bacteria, or viruses). However, there is still a paucity of comparative reports that critically evaluate the relative toxicity of carbon nanoallotropes in humans. This manuscript comprehensively reviews the biosensing applications of graphene and its derivatives (i.e. GO and rGO). Prospects and challenges are also introduced.

Dual-Mode Aptasensor Assembled by a WO3/Fe2O3 Heterojunction for Paper-Based Colorimetric Prediction/Photoelectrochemical Multicomponent Analysis

The programed bimodal photoelectrochemical (PEC)-sensing platform based on DNA structural switching induced by targets binding to aptamers was innovatively designed for the simultaneous detection of mucin 1 (MUC1) and microRNA 21 (miRNA-21). To promote excellent current intensity as well as enhance the sensitivity of aptasensors, the evenly distributed WO₃/Fe₂O₃ heterojunction was prepared as a transducer material, notably reducing the background signal response and extending the absorption of light. The multifunctional paper-based biocathode was assembled to provide a visual colorimetric assay. When introducing the integrated signal probe (ISP) composed of signal probe 1 (sP1) and signal probe 2 (sP2) on paper-based working units modified with gold nanoparticles (AuNPs), recognition sites of two targets were formed. In the presence of MUC1 protein, both sP1 and the target on the working unit were released into the corresponding colorimetric unit because of the DNA specific recognition. The horseradish peroxidase-streptavidin (HRP-SA) carried by free sP1 could oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to turn a blue-colored oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂), which ultimately gained a higher photocurrent signal. Furthermore, miRNA-21 was modified on another working unit by binding with sP2, leading to changes in the current signal and thus enabling real-time detection of analytes with the assistance of a digital multimeter. The PEC aptasensor offered a wide dynamic range of 10 fg·mL^-1-100 ng mL^-1 for MUC1 and 0.1 pM-10 nM for miRNA-21, with a low detection limit of 3.4 fg·mL^-1 and 36 fM, respectively. It laid the foundation for synchronous detection of multiple analytes and initiated a new way for the enhancement in modern next-generation disease diagnosis.

Au nanoparticle-loaded eggshell for electrochemical detection of nitrite

Eggshell is an extremely large source of domestic waste and has a huge scientific research potential because of its unique porous hierarchical structure. By converting eggshell waste into valuable functional materials, it can be recycled in many fields. Herein, we envisioned an economical and environmentally friendly conversion method for synthesizing Au nanoparticle loaded eggshell nanocomposites (defined as Au/CaCO3 nanocomposites) for the detection of trace amounts of nitrite in oolong tea. Compared with bare electrodes, the prepared Au/CaCO3 nanocomposite-based electrodes have obvious electrochemical enhancement behavior. A wide linear response range of 0.01 to 1.00 mM and a relatively low detection limit of 11.55 nM have been obtained in this study. The "turning waste into treasure" transformation strategy not only provides a practical and low-cost method for comprehensive utilization of eggshells as valuable functional materials, but also provides a new approach for sensitive detection of pollutants.

Surface engineering of carbon selenide nanofilms on carbon cloth: An advanced and ultrasensitive self-supporting binder-free electrode for nitrite sensing

Large uptakes of nitrite have been proven to be detrimental to human health, therefore, the development of high-performance nitrite sensors is highly emergent. Herein, a carbon selenide nanofilms modified carbon fiber cloth (CSe₂ NF/CC) electrode was obtained via in-situ synthesis to detect nitrite. The electrode integrates the collective merits of macroporous CC and pleated carbon selenide nanofilms, possessing a low overpotential of 0.83 V, a high electrochemical active surface area (EASA) of 5.39 cm², great electrical conductivity, and fast charge transport as well as ion diffusion. The proposed electrode achieved a low limit of detection of 0.04 μmol L^-1 (S/N = 3), a high sensitivity of 2048.56 μA mmol L^-1 cm^-2, excellent selectivity, and long-term stability. Additionally, the CSe₂ NF/CC was successfully used for nitrite detection in different food samples such as pickled vegetables and sausage samples.

Ultra-Weak Chemiluminescence Enhanced by Cerium-Doped LaF3 Nanoparticles: A Potential Nitrite Analysis Method

In this work, cerium-doped LaF₃ nanoparticles (LaF₃:Ce NPs) were successfully synthesized and characterized. Its chemiluminescence (CL) property was studied, and it was amazingly found that it intensely enhanced the ultra-weak CL of the NaNO₂-H₂O₂ system. The CL mechanism was systematically investigated and suggested to be the recombination of electron-injected and hole-injected LaF₃:Ce NPs. The new CL system was developed to be a facile, original, and direct method for nitrite analysis. Experimental conditions were optimized and then a satisfactory linear relationship between CL intensity and nitrite concentration was obtained. This work introduced a new pathway for the research and application of traditional fluoride NPs doped with RE³⁺.