Low Detection Limit Research Articles

High Performance H2S Sensor Based on Ordered Fe2O3/Ti3C2 Nanostructure at Room Temperature.

The utilization of a heterogeneous nanojunction design has shown significant enhancements in the gas sensing capabilities of traditional metal oxide gas sensors. In this study, a novel room temperature H2S gas sensor employing Fe2O3 functionalized Ti3C2 MXene as the sensing material has been developed. This sensor exhibits a broad detection range (0.01-500 ppm), low detection limit (10 ppb), and rapid response/recovery times (10 s/15 s), making it ideal for ppb-level H2S detection. The exceptional gas sensitivity of Fe2O3/Ti3C2 composite to H2S can be attributed to several key factors. First, the unique layered frame structure of Fe2O3/Ti3C2 significantly amplifies the surface area of the hybrid material, enhancing the absorption and diffusion capabilities of H2S molecules. Second, the abundance of functional groups (-O, -OH, and -F) on the surface of Ti3C2 MXene nanosheets provides additional active sites for H2S adsorption, The density functional theory calculation confirms that the adsorption energy of the Fe2O3/Ti3C2 composite for H2S (-2.93 eV) is significantly lower than that of pure Fe2O3 (-2.37 eV) and Ti3C2 (-0.2 eV). Lastly, the remarkable metal conductivity of Ti3C2 MXene ensures efficient electron transfer, thereby enhancing overall sensing performance.

Ti3C2Tx MXene‐Polyaniline Nanocomposite as an Adsorbent in Microextraction by Packed Sorbent for the Analysis of Parabens in Water and Juice Samples

ABSTRACTHerein, a novel Ti3C2Tx MXene and polyaniline nanocomposite is successfully synthesized and used for the highly efficient extraction of parabens. Polyaniline (PANI) nanofibers have formed a porous and peculiar π–π conjugated structure on hydrophilic MXene sheets, providing numerous adsorption sites for microextraction of analytes with moderate polarities such as parabens. The method is simple and sensitive, using microextraction by packed sorbent coupled with a high‐performance liquid chromatography‐ultraviolet detector. Under the optimal conditions, the method provides suitable preconcentrating factors of 28–35, ultrahigh sensitivity with low limits of detection of 0.3–0.5 µg/L, wide linearity of 0.3.0–200 µg/L with coefficients of determination ≥ 0.9983, and satisfactory precision with relative standard deviations ≤ 10.7%. The outstanding performance has been confirmed in well water and orange juice samples, with recoveries in the range of 93.1%–101.2% for water and 90.6%–103.4% for orange juice samples, respectively.

CuO@3D graphene modified glassy carbon electrode towards the detection of Orange II and Rhodamine B

Synthetic dyes are illegally used in foodstuffs and cause serious health issues in humans due to their carcinogenic nature. To avoid serious health issues, it is compulsory to detect and remove even the minute quantities of these harmful dyes in foodstuffs. Electrochemical sensors are accredited as an efficient and promising platform for the robust and sensitive determination of food toxins in various foodstuffs. Therefore, an efficient, facile, and competent sensor is devised for the simultaneous detection of Orange II (OR II) and Rhodamine B (RhB) supported by rGO and CuO nanoparticles. The synergism between rGO’s immense surface area and the adsorption properties of CuO enhances selectivity and response time for the detection of OR II and RhB. This work elaborated the synthesis, characterization, and electrochemical behavior of CuO@3DGr electrode towards simultaneous sensing of OR II and RhB. Physicochemical techniques were utilized to validate the fabrication of targeted material. On the other hand, the electrochemical features of the developed sensor were characterized by cyclic voltammetry (CV) and electron impedance spectroscopy (EIS). Differential pulse voltammetry technique was employed to detect simultaneously Orange II and Rhodamine B on the surface of bare (GCE), GO/GCE, CuO/GCE, and CuO@3DGr/GCE. Multi-analyte detection is possible with DPV, a sensitive electrochemical method. Based on each toxin’s specific electrochemical signature, the sensor may generate separate peaks by delivering a sequence of potential pulses and detecting the ensuing current. The parameters which influence the performance of the modified sensor were carefully evaluated. Under ambient conditions, the developed sensor exhibited excellent electrocatalytic activity in oxidation at 0.67 V of OR II and 0.96 V RhB with a low limit of detection 08 nM for OR II and 4.5 nM for RhB in Britton- Robinson buffer (BRB pH:7). The described methodology allowed a robust and fast analysis of food toxins in different foodstuff establishing this sensor as a novel tool for detecting food toxins. Tap water was used to analyze the practical applicability of developed electrode material and suitable results were achieved. These results showed that the as-synthesized novel electrochemical sensor has the potential for ultrasensitive determination and detection of toxins in different foodstuffs.

The Promise of Carbon Nano‐Onions: Preparation, Characterization and Their Application in Electrochemical Sensing

AbstractCarbon nano‐onions (CNOs) promise to improve the range of applications of carbon materials for electroanalytical applications. In this review, we explore the synthesis, characterization, and electrochemical applications of CNOs. CNO‐based sensors present impressive features, including low detection limits in the femtogram per milliliter range, a broad linear detection range spanning up to 7 orders of magnitude, exceptional selectivity, reproducibility, and stability. Synthetic methods and characterization techniques for CNOs were thoroughly examined, shedding light on their pivotal role in biosensing technologies. Comparative analyses with other carbon materials underscore CNOs′ competitive performance, either surpassing or matching many counterparts. Despite their relatively recent integration in biosensing applications, CNOs exhibit comparable or superior results concerning other carbon‐based materials. Indeed, the incorporation of CNOs into hybrid nanocomposites has shown promising outcomes, indicating a synergistic potential for future advancements in biosensing technologies. Our review provides a broad approach to the application of CNOs to the field, with emphasis on breakthroughs of the last 5 years.

Preparation and application of a new ion-imprinted polymer for nanomolar detection of mercury(II) in environmental waters

This study introduces a novel ion-imprinted polymer for the ultrasensitive detection of mercury(II) in water. The ion-imprinted polymer was synthesized via a simple bulk polymerization process using methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, morpholine-4-carbodithioic acid phenyl ester as the chelating agent, and ammonium persulfate as the initiator. The electrochemical mercury(II) sensing capability of the ion-imprinted polymer was studied via the modification of a cost-effective carbon paste electrode. A stripping voltammetric technique was utilized to quantify the analyte ions following open-circuit enrichment. Critical experimental parameters, including the nature and concentration of the eluent, solution pH, preconcentration duration, ion-imprinted polymer dosage, sample solution volume and reduction potential, were systematically studied and optimized. Under optimal conditions, the sensor exhibited a linear response in the range of 1.0 to 240.0 nM, with a low detection limit of 0.2 nM. The sensor demonstrated remarkable selectivity against potential interfering ions, including lead(II), cadmium(II), copper(II), zinc(II), manganese(II), iron(II), magnesium(II), calcium(II), sodium(I) and cobalt(II). The practical applicability of the developed method was successfully validated through the analysis of real water samples, suggesting its potential for environmental monitoring applications.

Dual Recognition Strategy-Based Ratiometric Electrochemical Assay for Ultrasensitive and Accurate Detection of Specific Circulating Tumor Cells.

Sensitive, specific, and accurate detection of circulating tumor cells (CTCs) is of great importance in the diagnosis and prognosis of cancer. Herein, an ultrasensitive ratiometric electrochemical biosensor was designed with a dual recognition strategy for highly specific and accurate detection of circulating MCF-7 human breast cancer cells based on gold film-modified porous organic cages loaded with ferrocene (Au/Fc@POCs) as the substrate and methylene blue-encapsulated covalent organic frameworks (MB@COFs) as the label material, producing two independent electrochemical signals from the Fc and MB probes, respectively. As the concentration of MCF-7 cells increases, the electrochemical signal of MB enhances significantly while the oxidation signal of Fc decreases remarkably. Under optimal experimental conditions, the ratios (IMB/IFc) between the double signals showed a broad dynamic range of 10 to 1 × 107 cells/mL with an effectively lower detection limit of 1 cells/mL (S/N = 3). Furthermore, the biosensor was able to accurately enumerate MCF-7 cells in human serum samples with excellent results. In this work, the developed ratiometric electrochemical biosensor offers a reliable and sensitive strategy for the quantitative determination of circulating MCF-7 human breast cancer cells as well as an effective approach for the clinical detection of rare cancer cells, especially in early stage cancer diagnosis.

Fabrication of a novel mixed-valent copper-based coordination polymer as a fluorescent sensor for selective and efficient detection of multiple analytes

A novel three-dimensional fluorescent mixed-valent copper-based coordination polymer (CP), namely {[CuICuII4(triazol)6(bpta)2]Cl}n (Cu-CP), was synthesized hydrothermally in the presence of Cu(II) ion, 2,4,6-tri(1H-1,2,4-triazol-1-yl)-1,3,5-triazine (TTT), and 2,2′,4,4′-biphenyltetracarboxylic acid (H4bpta). The structure of the Cu-CP was studied using single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD). Interestingly, the crystallographic data revealed that a part of Cu(II) ions were reduced in situ to Cu(I) ions as well as the nitrogen-containing ligand TTT was converted to triazol, which possessed excellent fluorescence characteristics as a transition metal ion with a d10 electronic configuration, prompting further investigation into the fluorescence sensing properties of Cu-CP. The results confirmed that Cu-CP exhibited excellent fluorescence performance which an outstanding candidate as a fluorescence sensor for Fe3+, Cr2O72−, CrO42−, MnO4− and nitrobenzene (NB), with a low limit of detection. For ethylene glycol (EG) detection, Cu-CP showed high-efficiency fluorescence enhancement across a range of temperatures. The underlying mechanism of fluorescence enhancement was investigated through comprehensive experimental studies.

Modified perylene diimide for femto molar level detection of glucose: smartphone-assisted colorimetric glucose detection kits.

In this report, a functionalized hydroxyphenyl benzothiazole (HBT) derivative has been synthesized and anchored onto the perylene diimide (PDI) core at the -bay position (PHI). PHI has been explored for the generation of radical anions (PH1˙-) and dianions (PH12-) in 20% HEPES buffer-DMSO solution using H2S as a sacrificial electron donor. The PH1˙- has a half-life (t1/2) of 1.5 h and 3 h in oxygenated and hypoxic conditions, respectively. The formation of radical anions has been confirmed by optical (absorbance and fluorescence) methods, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and femtosecond transient absorbance spectroscopy along with current-voltage (I-V) and NOBF4 studies. The PH1˙- showed peroxidase-like activity for the reduction of H2O2 as low as 170 fmol L-1 (fM) giving a colour change from sea green to pink. The biochemical assay which consists of PH1˙-+ GOx has been further utilized as a glucose sensor. Upon addition of glucose (0-8 nM) in the biochemical assay, the in-situ produced H2O2 (after oxidation of glucose with GOx) oxidized PH1˙- to PH1 giving a sea green to pink colorimetric read out along with a decrease in the absorption intensities at 720, 815, 880 and 950 nm and the emergence of absorption intensity at 541 nm. The lowest limit of detection is 85 fM. We also explored this biochemical assay for the detection of 860 fM of glucose in a 10% blood serum. Similarly, fluorometric, CV and DPV studies were carried out for the detection of glucose using this biochemical assay. The smartphone-assisted RGB colour analyser showed large variations in the red colour and this RGB based colour differentiation can be used for the detection of 1 nM of glucose.

The First N,O-Chelated Diphenylboron-Based Fluorescent Probe for Peroxynitrite and Its Bioimaging Applications

Peroxynitrite (ONOO−) is a reactive oxygen species (ROS) that takes part in the oxidation-reduction homeostasis while at the same time being responsible for activating numerous pathological pathways. Accordingly, monitoring the dynamic changes in ONOO− concentration has attracted a great deal of attention, undoubtedly prompting the development of appropriate fluorescent chemosensors. Herein, we developed a novel N,O-chelated diphenylboron-based fluorescent probe (DPB) for ONOO− featuring high selectivity, a quick response time (2.0 min), and a low detection limit (55 nM). DPB incorporates tetra-coordinated boron in the center of the fluorogenic core and a three-coordinated boron from the pinacolphenylboronate fragment, which acts as the recognition site for ONOO−. As confirmed by HR-MS and 1H NMR, the interaction of DPB with ONOO− led to an oxidative cleavage of pinacolphenylboronate moiety to produce strongly emissive derivative DPB-OH. The fluorescence enhancement is likely a result of a substantial deactivation of non-radiative decay due to the replacement of the bulky pinacolphenylboronate moiety with a compact hydroxyl group. Importantly, DPB probe exhibits negligible cytotoxicity and favorable biocompatibility allowing for an efficient tracking of ONOO− in living cells and zebrafish. Overall, the current study does not only represents the first N,O-chelated diphenylboron-based fluorescent probe for a specific analyte, but also serves as a guideline for designing more potent fluorescent probes based on the chemistry of boron chelates.

Highly conductive and sensitive alginate hydrogel strain sensors fabricated using near-field electrohydrodynamic direct-writing process

Hydrogel flexible sensors have attracted considerable attention because of their wearability, biocompatibility, and precision signal transmission capability. However, the hydrogel strain sensors fabricated by conventional printing or hand-injection methods have difficulty balancing their mechanical strength and sensing characteristics, limiting the application of hydrogel strain sensors. Herein, polyvinyl alcohol and polyacrylamide were loosely crosslinked with sodium alginate through chemical cross-linking. Subsequently, MXene nanosheets were introduced for doping, the crosslinked hydrogel conductive network was constructed, and the hydrogel strain sensors were fabricated using the electrohydrodynamic (EHD) printing method. The ions in the EHD-printed hydrogel undergo directional movement under an externally enhanced electric field, causing the formation of more uniform and dense porous conductive networks inside the hydrogel, and high electrical conductivity (0.49 S m−1) is obtained. These hydrogel strain sensors have excellent mechanical properties (tensile strength: 0.17 MPa at 787 % strain), high sensitivity (gauge factor: 1.54 at 0–100 % strain), and low detection limits (1 % strain). Furthermore, demonstrations of real-time Morse code tapping information transmission, handwriting recognition during writing, and human physiological behavior monitoring demonstrations using the fabricated sensors indicate that the EHD-printed hydrogel strain sensor method has significant potential for wearable devices and human-computer interaction applications.

Environmentally Benign Synthesis of Magnetic Fe3O4 Nanoparticle/Carbon Black/Copper‐Quercetin Rods for Sensitive, Disposable Electrochemical Sensor for Mitoxantrone

AbstractPhenolic compounds have a variety of activities but are most famous for their antioxidant and metal‐chelating properties. We explore the green synthesis and application of Fe3O4 nanoparticles, carbon black (CB), and copper‐quercetin (Cu−Q) composite for a disposable electrochemical sensor for mitoxantrone. Fe3O4 was synthesised using Camellia sinensis leaf extract. The copper‐quercetin was synthesised by titrating copper acetate solution with quercetin monohydrate solution at room temperature. Equal amounts of Fe3O4, CB, and Cu−Q were mixed to form Fe3O4‐CB/Cu−Q. The Fe3O4‐CB/Cu−Q/SPE has the lowest detection limit (55.47 pM) compared to previous mitoxantrone sensors. The average recovery was 102.2 %, with an RSD of 4.67 % in serum. The sensor maintained an average accuracy of 98.99 % in the presence of the interfering agent. The detection limit of the new sensor is about five times lower than that of the previous Fe3O4 and carbon black electrode. Therefore, it can be suggested that the Copper‐quercetin complex contributed significantly to the electrode's sensitivity. This research is the first to report the three oxidation potentials for mitoxantrone consistent with mitoxantrone's complex oxidation mechanism. Also, this is the first report on using copper‐quercetin as an electrode material for electrode chemical detection. Furthermore, this is the first green‐derived sensor for mitoxantrone.

Revitalizing E-waste: Eco-friendly electrochemical sensor for Hg(II) detection enhanced by oxygen vacancy in metal oxide nanostructures based on recycled LCD

In the current work, an innovative eco-friendly sensor using ceria integrated cobalt oxide nanosheets immobilized on LCD monitor (Ce@Co-EcoR) recycled from E-waste is presented. The Ce@Co-EcoR nanocomposite was thoroughly investigated using appropriate characterization techniques. This nanostructured electrode was employed to construct an electrochemical sensor to detect mercury. It showed a very low detection limit of 2.8 ppb, a wide detection ranges from 16 to 620 ppb, and a good sensitivity of 158.28 μA cm2.ppm−1. The sensor applicability was verified by performing interference, repeatability, stability studies. It was also applied to control the purity of sea water. This work underscores the potential of incorporating recycled materials onto sensor technology, not only to control environmental pollution, but also to promote sustainable practices in scientific innovation.

Gold-enhanced aptasensors for highly sensitive dengue detection: a cost-effective approach

The reemergence of diseases such as Dengue has spurred the development of efficient biosensing devices. This study aims to establish a rapid, cost-effective, and efficient platform for Dengue detection. The surface of the sensor was constructed by sputtering gold onto fluorine-doped tin oxide thin films, that were previously deposited on glass substrates. Varied sputtering deposition times were used. Results obtained from X-Ray Diffraction analysis showed that the films with 4-minute deposition time had the best gold surface coverage and the best cost-benefit ratio for sensor fabrication. Subsequently, the gold thin films were functionalized with the co-immobilization of a self-organized monolayer of aptamers and 6-mercapto-1-hexanol (MCH). The monolayer was analysed using the electrochemical impedance spectroscopy technique, and the ratio of 1:25 (aptamer: total thiol) was determined for surface optimization. The performance of the aptasensor was tested for the detection of the non-structural protein 1 of Dengue serotype 4 (NS1-S4). A good sensitivity of 40.2 ± 3.7 % per decade and a low detection limit of 1.25 pg/mL were obtained. The development of this platform represents an advance in the fast fabrication of aptasensors for the detection of emerging diseases such as Dengue, contributing also to the miniaturization process of point-of-care devices.

A Metal-Organic Framework-Based Colorimetric Sensor Array for Transcutaneous CO2 Monitoring via Lensless Imaging

Transcutaneous carbon dioxide (TcPCO2) monitoring provides a non-invasive alternative to measuring arterial carbon dioxide (PaCO2), making it valuable for various applications, such as sleep diagnostics and neonatal care. However, traditional transcutaneous monitors are bulky, expensive, and pose risks such as skin burns. To address these limitations, we have introduced a compact, cost-effective CMOS imager-based sensor for TcPCO2 detection by utilizing colorimetric reactions with metal–organic framework (MOF)-based nano-hybrid materials. The sensor, with a colorimetric sensing array fabricated on an ultrathin PDMS membrane and then adhered to the CMOS imager surface, can record real-time sensing data through image processing without the need for additional optical components, which significantly reduces the sensor’s size. Our system shows impressive sensitivity and selectivity, with a low detection limit of 26 ppm, a broad detection range of 0–2% CO2, and strong resistance to interference from common skin gases. Feasibility tests on human subjects demonstrate the potential of this MOF-CMOS imager-based colorimetric sensor for clinical applications. Additionally, its compact design and responsiveness make it suitable for sports and exercise settings, offering valuable insights into respiratory function and performance. The sensing system’s compact size, low cost, and reversible and highly sensitive TcPCO2 monitoring capability make it ideal for integration into wearable devices for remote health tracking.

Improved the Sensitivity and Limit of Detection of Surface Alloying SERS Sensors by Controlling Mixing Ratio of Trimetallic (Ag-Au-Pd) Nanoparticles

In this study, three different types of hybrid structures SERS sensors made from different mixing ratio of trimetallic (Ag-Au-Pd) nanoparticles of [Au1: Ag1: Pd1] , [Au1: Ag2: Pd1] , [Au1: Ag2: Pd2] in surface alloying forms deposited on macro porous silicon (macroPsi) layer were created and extensively tested. By using a simple and fast immersion process, trimetallic (Ag-Au-Pd) nanoparticles were created utilizing ion reduction of numerous metallic salts on a macro porous silicon (macroPsi) layer. The macroPsi layers were created using a laser assisted etching (LAE) technique for 15 minutes with a constant density of approximately (28mA/c.m2). At a constant concentration (10-3 M) of HAu.Cl4, Ag.NO3 and Pd.Cl2 to synthesize Au-NPs, Ag-NPs and Pd-NPs, immersion processes with various mixing ratios were performed. The hybrid structures of SERS sensors were examined using XRD, FE-SEM, and Raman microscopes. The sensors were tested at different concentrations from 10-6 to 10-12 of MB target molecules. The SERS trimetallic sensors demonstrated a considerable reliance on hot spot zones among trimetallic nanoparticles. Higher enhancement factor with lower detection limit of Raman signal was obtained from [Au1: Ag2: Pd2] hybrid structures SERS sensor of about 1.5×1010 and 10-14 respectively, due to extra ordinary specific surface area and high surface density forming trimetallic nanoparticles . The variations of mixing ratio of trimetallic (Ag-Au-Pd) provide an effective pathway to develop the sensors performance towards detection of lower concentrations.

High-performance PANI sensor on silicon nanowire arrays for sub-ppb NH3 detection

For industrial production and disease diagnosis, real-time detection of low concentrations of NH3 is crucial, necessitating a gas-sensitive sensor compatible with integrated processes and exhibiting excellent performance. Herein, we employed wet etching and rapid in-situ polymerization on silicon nanowire substrates to grow polyaniline fibers, thereby fabricating NH3 gas sensors with p-p heterojunction and three-dimensional network structures. Characterization and gas sensing performance testing were conducted. The results demonstrate the outstanding NH3 detection capabilities of the sensor, providing stable responses down to concentrations as low as 1 ppb, which indicates its LOD is one to two orders of magnitude lower than current similar products. It also exhibits verified selectivity and long-term reliability. The excellent sensing performance is attributed to the high surface area from the silicon nanowire structure and efficient synergy of p-p heterojunction. Additionally, the influence of doping types of the substrates and annealing process were explored. This work serves as a reference for the design of silicon-based gas sensors with high sensitivity, low detection limits, and extended operational lifetimes, suitable for deployment in commercial integrated monitoring systems.

Spontaneous Cooling Enables High-Quality Perovskite Wafers for High-Sensitivity X-Ray Detectors with a Low-Detection Limit.

Developing high-quality perovskite wafers is essential for integrating perovskite technology throughout the chip industry chain. In this article, a spontaneous cooling strategy with a hot-pressing technique is presented to develop high-purity, wafer-scale, pinhole-free perovskite wafers with a reflective surface. This method can be extended to a variety of perovskite wafers, including organic-inorganic, 2D, and lead-free perovskites. Besides, the size of the wafer with diameters of 10, 15, and 20 mm can be tailored by changing the mold. Furthermore, the mechanism of spontaneous cooling for improving the quality of perovskite wafers is revealed. Finally, the high-quality lead-free Cs3Cu2I5 perovskite wafers demonstrate excellent X-ray detection performances with a high sensitivity of 3433.6 µC Gyair -1 cm-2 and a low detection limit of 33.17 nGyair s-1. Moreover, the Cs3Cu2I5 wafers exhibit outstanding environmental and operational stability even without encapsulation. These research presents a spontaneous cooling strategy to achieve wafer-scale, high-quality perovskites with mirror-like surfaces for X-ray detection, paving the way for integrating perovskites into electronic and optoelectronic devices and promoting the practical application of perovskite X-ray detectors.

Sustainable synthesis of MOF for COVID-19 detection using a 23 factorial design

The emergence of the COVID-19 pandemic has underscored the urgent requirement for rapid and accurate diagnostic methods to detect the virus and control its spread. Metal Organic Frameworks (MOFs) have gained significant interest in biosensing applications because of their exceptional properties. This study investigates the microwave synthesis of zeolitic imidazolate framework-8 (ZIF-8) and explores its potential as a fluorescent biosensor for detecting COVID-19 RNA sequences. The microwave method enables a rapid, eco-friendly, and efficient synthesis of ZIF-8. Characterization tests including PXRD, FE-SEM, TGA, and FT-IR confirmed the high crystallinity and thermal stability of ZIF-8. To optimize the biosensor’s performance, a 23 factorial design is pursued. The factorial design allows determining the individual and simultaneous effects of the control parameters such as ZIF-8 concentration, buffer pH, and solution temperature on the quenching efficiency. The results demonstrate that the parameters combination of 25 °C, pH 8.0, and 0.7 mg/mL ZIF-8 concentration results in the highest quenching percentage of 72.41 %. The study of the quenching mechanism confirms that the P-DNA can form electrostatic and π-π stacking interactions with ZIF-8, to produce a P-DNA@ZIF-8 complex. It is also found that photoinduced electron transfer is more dominant than fluorescence resonance energy transfer in the quenching mechanism. The biosensor showed a high sensitivity towards the target COVID-19 RNA with a very low detection limit of 12.02 pM, a fast detection time of 40 minutes, and high selectivity to the target RNA. This study shows the potential of ZIF-8 as a feasible and environmentally friendly material for swiftly and accurately detecting COVID-19 RNA sequences.

Self-supported electrochemical sensor based on uniform palladium nanoparticles functionalized porous graphene film for monitoring H2O2 released from living cells.

Graphene film has been considered a promising material for the construction of self-supported electrodes due to its favorable flexibility and high conductivity. However, the film fabricated from pristine graphene or conventional graphene sheet reduced graphene oxide processes limited electrocatalytic performance. Decorating active metal species or incorporating heteroatoms intothegraphene framework have been proved to be effective methods to enhance the electrocatalytic efficiency of graphene film-based self-supported electrodes. Herein, we present a freestanding electrode composed of uniform Pd nanoparticles decorating N,S co-doped porous graphene film (Pd/NSPGF) and explore its practical application in differentiating various human colon cell types by in situ tracking the amount of H2O2 secreted from live cells. Our findings reveal that, on the one hand, the NSPGF has abundant surface and inner pores, which promote active site exposure, and mass diffusion during electrochemical reactions; on the other hand, the substitutional doping ofthe graphene framework with heteroatoms (e.g., N or S) can tailor its electronic and chemical properties, and facilitate the uniform loading of high-density Pd nanoparticles. Moreover, the intrinsic activity of Pd/NSPGF is regulated by the interaction of Pd nanoparticles withtheNSPGF support. Taking the advantages of morphology and composition, the self-supported Pd/NSPGF electrode displays remarkable electrochemical performance with a wide linear range up to 2.0mM, low detection limit of 0.1μM (S/N = 3), high sensitivity of 665 µA cm-2mM-1, and good selectivity. When applied in real-time trackingofthe H2O2 released from normal human colon epithelial cells and human colorectal cancer cells, the Pd/NSPGF-based electrochemical sensing system can distinguish the cell types by testing the number of extracellular H2O2 molecules released per cell, which holds considerable potential for early detection and monitoring of disease-related clinical specimens.

Nonstoichiometry Promoted Solventless Recrystallization of a Thick and Compact CsPbBr3 Film for Real-Time Dynamic X-Ray Imaging.

Inorganic CsPbBr3 perovskite emerges as a promising material for the development of next-generation X-ray detectors. However, the formation of a high-quality thick film of CsPbBr3 has been challenging due to the low solubility of its precursor and its high melting point. To address this limitation, a nonstoichiometry approach is taken that allows lower-temperature crystallization of the target perovskite under the solventless condition. This approach capitalizes on the presence of excess volatile PbBr2 within the CsPbBr3 film, which induces melting point depression and promotes recrystallization of CsPbBr3 at a temperature much lower than its melting point concomitant with the escape of PbBr2. Consequently, thick and compact films of CsPbBr3 are formed with grains ten times larger than those in the pristine films. The resulting X-ray detector exhibits a remarkable sensitivity of 4.2 × 104 µC Gyair -1 cm-2 and a low detection limit of 136 nGyair s-1, along with exceptional operational stability. Notably, the CsPbBr3-based flat-panel detector achieves a high resolution of 0.65 lp pix-1 and the first demonstration of real-time dynamic X-ray imaging for perovskite-based devices.