Low Detection Limit Research Articles

Aptamer-regulated colorimetric and electrochemical dual-mode sensor for the detection of uranyl ions utilizing AuNCs@COF composite.

Uranium is the core material for the development of the nuclear industry, but its irreversible radiation damage poses a significant threat to human health. In this context, an innovative dual-mode colorimetric and electrochemical sensor was developed for the detection of uranyl ions (UO22+), utilizing a covalent organic framework@gold nanoclusters (AuNCs@COF) composite. The synthesis of AuNCs@COF was simple, and the incorporation of AuNCs imparted the composite with exceptional peroxidase-like catalytic activity and enhanced electrochemical properties. By regulating the adsorption and desorption of aptamers on the AuNCs@COF surface, both peroxidase-like activity and conductivity were modulated, enabling the detection of UO22+ utilizing colorimetric and electrochemical dual signals. Under optimal conditions, the sensor revealed a broad linear detection range and a low detection limit, with ranges of 1.36 × 10-10-1.36 × 10-5mol/L for colorimetric detection and 5.0 × 10-10-2.5 × 10-5mol/L for electrochemical detection, achieving detection limitsfor these two methodsof 107 pmol/L and 347 pmol/L, respectively. Unlike other single-mode sensorsfor UO22+ detection, this dual-mode sensor demonstrated superior sensitivity, specificity, and repeatability. Furthermore, the results of spiked recovery experiments in real water samples highlight the promising potential of this dual-mode sensor for environmental water monitoring applications.

Organic Cation Modulation in Hybrid Zirconium Halides for High-Performance Flexible X-ray Imaging.

Exploiting novel materials featuring high-quality zero-dimensional structure, remarkable lattice stability, and minimal defects represents an efficacious strategy for enhancing the detection performance of X-ray scintillators. Here, we design and synthesize two novel, lead-free, zirconium-based zero-dimensional organic-inorganic hybrid metal halides (OIMHs), C14H40N4ZrCl8 and C6H16N2ZrCl6. Based on the steric hindrance effect of organic cations, the distance between [ZrCl6]2- polyhedra was designed and the electronic coupling interactions among polyhedra were adjusted, thus precisely engineering excellent zero-dimensional materials. Simultaneously, the stronger N-H+···Cl- (interstitial) bond is introduced to avoid structural instabilities and more defects due to the bigger organic cation in C14H40N4ZrCl8. As expected, C14H40N4ZrCl8 exhibits more remarkable luminescence behavior compared to C6H16N2ZrCl6 when excited by UV light and X-rays. The photophysics process involving self-trapped excitons and defects is elaborately expounded using first-principles calculations, luminescence properties, and stabilities. Finally, a flexible and large-area scintillation screen with a size of up to 200×100 mm2 based on C14H40N4ZrCl8 is fabricated and attains a high spatial resolution of 21.35 lp mm-1 and a lower limit of detection of 2.270 μGyair s-1, outperforming the resolution of most blue-emitting scintillation screens. These results imply that the zirconium-based OIMHs possess significant potential applications for medical diagnostics, security scanning, and non-destructive testing.

Electrochemiluminescence imaging for immunoassay of prostate-specific antigen utilizing AIE-active polymer dots as the probe.

We report, for the first time to the best of our knowledge, an electrochemiluminescent (ECL) immunosensor for the imaging analysis of prostate-specific antigen, using aggregation-induced-emission-active polymer dots (Pdots) as emitters. Assisted by rolling circle amplification, the immunosensor exhibits high sensitivity, with a low detection limit of 4.2 pg mL-1. This work demonstrates the potential of AIE-active Pdots in clinical applications.

SERS-Based Immunochromatographic Assay for Sensitive Detection of Escherichia coli O157:H7 Using a Novel WS2-AuDTNB Nanotag

E. coli O157:H7 contamination in food and the environment poses a serious threat to human health. Rapid and sensitive identification of foodborne pathogens remains challenging. Here, we prepared tungsten disulfide (WS2)–Au nanocomposites coupled with the Raman signal molecule 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB) and antibodies to replace the conventional colloidal gold nanoparticles and applied SERS-active nanotags in the SERS-ICA method for highly sensitive detection of E. coli O157:H7. The large surface area and numerous effective SERS hotspots of WS2-Au nanotags provide superior SERS signals. Under optimized conditions, this ICA achieves the quantitative detection of E. coli O157:H7 in a broad linear range of 8 × 102–8 × 107 CFU/mL and at a low detection limit of 175 CFU/mL. In addition, the test strip indicates high specificity for E. coli O157:H7 identification, favorable reproducibility, and shows good accuracy in the detection of actual food samples, such as milk and pork. The proposed assay can be used for rapid qualitative and quantitative detection of E. coli O157:H7 and has great potential for field application.

Integration of Carboxylate Carbon Dot-Supported Gold Nanoparticles with Boron Nitride Nanosheets for Electrochemical Sensing of Prostate-Specific Antigen via Sandwich Immunoassays.

An electrochemical sandwich immunoassay was fabricated to measure the prostate-specific antigen (PSA) biomarker. The PSA immunosensor was developed by altering the surface of a glassy carbon electrode (GCE) with a nanocomposite comprising carboxyl-functionalized carbon dots that support gold nanoparticles (AuNPs), which were then combined with hydroxylated boron nitride nanosheets (HO-BN). This construction possesses distinctive signal enhancement characteristics and was prepared via a facile method. Considering the high biological affinity of AuNPs for biomolecules, carbon dots (CDs) with carboxyl (COOH) groups make a suitable substrate for electrode modification. This alteration allows for the PSA antibody (Ab1) attachment, resulting in a sandwich-like configuration. Additionally, carbon dot-stabilized AuNPs integrated into HO-BN nanosheet nanocomposites considerably boost the electron transfer rate, leading to remarkable potential in sensor applications. By utilizing horseradish peroxidase (HRP)-conjugated antifree PSA antibody (Ab2), a reduction in hydrogen peroxide (H2O2) was achieved within the electrochemical cell. This reduction led to increased current, attributed to the increased PSA concentration, which is required for the biosensor analysis to perform properly. The developed immunosensor revealed a linear correlation with PSA concentrations ranging from 1.0 to 3500 pg mL-1, achieving a low detection limit of 0.136 pg mL-1. Furthermore, the PSA aptasensor demonstrates excellent selectivity, remarkable stability, and commendable reproducibility, indicating its significant potential for clinical research and diagnostic applications.

Conformationally Locked Peptide‐DNA Nanostructures for CRISPR‐Amplified Activity‐Based Sensing

We introduce a new class of chemical probes for activity‐based sensing of proteases, termed Cleavable, Locked Initiator Probes (CLIPs). CLIPs contain a protease‐cleavable peptide linked between two programmable DNA strands – an “initiator” DNA and a shorter “blocking” DNA. These DNA sequences are designed to hybridize, creating a “locked” hairpin‐like structure. Upon proteolytic cleavage, the initiator strand is released, triggering the activation of CRISPR‐Cas12a enzymes and producing an amplified fluorescence response. CLIPs generate more than 20‐fold turn‐on signals at room temperature (25°C), significantly outperforming commercial probes by yielding ~40‐fold lower limits of detection (LOD) at 100‐fold lower concentrations. Their versatility enables the detection of various disease‐relevant proteases – including the SARS‐CoV‐2 main protease, caspase‐3, matrix metalloproteinase‐7, and cathepsin B – simply by altering the peptide sequence. Importantly, CLIPs detect cathepsin B in four different colorectal cancer cell lines, highlighting their clinical potential. Taken together, the sensitivity (LOD: ~88 pM), selectivity, and rapid assay time (down to 35 minutes), combined with the ability to operate in complex biological media with minimal sample preparation, position CLIPs as powerful chemical tools for activity‐based sensing of functional enzymes.

Conformationally Locked Peptide-DNA Nanostructures for CRISPR-Amplified Activity-Based Sensing.

We introduce a new class of chemical probes for activity-based sensing of proteases, termed Cleavable, Locked Initiator Probes (CLIPs). CLIPs contain a protease-cleavable peptide linked between two programmable DNA strands - an "initiator" DNA and a shorter "blocking" DNA. These DNA sequences are designed to hybridize, creating a "locked" hairpin-like structure. Upon proteolytic cleavage, the initiator strand is released, triggering the activation of CRISPR-Cas12a enzymes and producing an amplified fluorescence response. CLIPs generate more than 20-fold turn-on signals at room temperature (25°C), significantly outperforming commercial probes by yielding ~40-fold lower limits of detection (LOD) at 100-fold lower concentrations. Their versatility enables the detection of various disease-relevant proteases - including the SARS-CoV-2 main protease, caspase-3, matrix metalloproteinase-7, and cathepsin B - simply by altering the peptide sequence. Importantly, CLIPs detect cathepsin B in four different colorectal cancer cell lines, highlighting their clinical potential. Taken together, the sensitivity (LOD: ~88 pM), selectivity, and rapid assay time (down to 35 minutes), combined with the ability to operate in complex biological media with minimal sample preparation, position CLIPs as powerful chemical tools for activity-based sensing of functional enzymes.

Novel Amperometric Sensor Based on Glassy Graphene for Flow Injection Analysis

Flow injection analysis (FIA) is widely used in drug screening, neurotransmitter detection, and water analysis. In this study, we investigated the electrochemical sensing performance of glassy graphene electrodes derived from pyrolyzed positive photoresist films (PPFs) via rapid thermal annealing (RTA) on SiO2/Si and polycrystalline diamond (PCD). Glassy graphene films fabricated at 800, 900, and 950 °C were characterized using Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) to assess their structural and morphological properties. Electrochemical characterization in phosphate-buffered saline (PBS, pH 7.4) revealed that annealing temperature and substrate type influence the potential window and double-layer capacitance. The voltammetric response of glassy graphene electrodes was further evaluated using the surface-insensitive [Ru(NH3)6]3+/2+ redox marker, the surface-sensitive [Fe(CN)6]3−/4− redox couple, and adrenaline, demonstrating that electron transfer efficiency is governed by annealing temperature and substrate-induced microstructural changes. FIA with amperometric detection showed a linear electrochemical response to adrenaline in the 3–300 µM range, achieving a low detection limit of 1.05 µM and a high sensitivity of 1.02 µA cm−2/µM. These findings highlight the potential of glassy graphene as a cost-effective alternative for advanced electrochemical sensors, particularly in biomolecule detection and analytical applications.

Waveguide microwave gas sensor based on monolithic In2O3 for enhanced ammonia detection.

Waveguide microwave gas sensor based on monolithic In2O3 for enhanced ammonia detection.

Electrochemical immunoplatform for the quantification of epithelial extracellular vesicles applied to prostate cancer diagnosis.

Electrochemical immunoplatform for the quantification of epithelial extracellular vesicles applied to prostate cancer diagnosis.

Robustness and Efficiency Considerations When Testing Process Reliability with a Limit of Detection

Processes in biotechnology are considered reliable if they produce samples satisfying regulatory benchmarks. For example, laboratories may be required to show that levels of an undesirable analyte rarely (e.g., in less than 5% of samples) exceed a tolerance threshold. This can be challenging when measurement systems feature a lower limit of detection, rendering some observations left-censored. We investigate the implications of detection limits on location-scale model-based inference in reliability studies, including their impact on large and finite sample properties of various estimators and the sensitivity of results to model misspecification. To address the need for robust methods, we introduce a flexible weakly parametric model in which the right tail of the response distribution is approximated using a piecewise-constant hazard model. Simulation studies are reported that investigate the performance of the established and proposed methods, and an illustrative application is given to a study of drinking can weights. We conclude with a discussion of areas warranting future work.

Sensitive Detection of Aflatoxin B1 in Foods Using Aptasensing Based on FGO-Mediated CdTe QDs

Aflatoxin B1 (AFB1) exhibits high toxicity and has the potential to induce cancer, deformities, and mutations. It is therefore highly desirable that sensitive and straightforward methods for detecting AFB1 be developed. In this study, due to the high specific adsorption capacity of AFB1 aptamers, we applied a sensing strategy based on quantum dots (QDs) and carboxyl-functionalized graphene oxide (FGO) to construct a simple fluorescence quenching platform. FGO and CdTe QDs modified with AFB1 aptamers cause a FRET effect that produces CdTe QDs with yellow-green fluorescence quenching. When AFB1 is present, aptamers form complexes with it and CdTe QDs leave the quenching platform, resulting in fluorescence recovery. In this study, we used a fluorescence aptasensor with a wide detection range of 0.05 to 150 ng/mL and a low limit of detection (LOD) of 8.2 pg/mL. The average recoveries of AFB1 in peanut and pure milk samples ranged from 94.5% to 107.0%. The aptasensor also exhibited the advantages of simple operation, low cost, and good stability. The sensing strategy reported here can thus serve as a potential candidate for the rapid detection of AFB1.

GO-SELEX-enhanced dual-recognition sensor for highly specific detection of azamethiphos.

GO-SELEX-enhanced dual-recognition sensor for highly specific detection of azamethiphos.

UiO-66/ZIF-67/PEDOT Modified Glassy Carbon Electrode for Electrochemical Detection of Cu2+ and Hg2+ in Environmental Water

Abstract ZIF-67 and UiO-66 are different metal-organic framework (MOFs) materials widely used in gas adsorption, energy storage, catalysis, and electrochemical sensing due to their unique pore structure and chemical properties. Here, UiO-66/ZIF-67/PEDOT material modified glassy carbon electrode was prepared, and Cu2+ and Hg2+ in water were detected by electrochemical method (differential pulse voltammetry). ZIF-67 grows in flakes on the surface of UIO-66, and the two formed a synergistic effect, improving the selectivity and sensitivity of the detection. In addition, by coating a PEDOT film on the surface of the binary MOF, the conductivity of the material is further enhanced, thereby greatly improving the detection sensitivity. Under the optimized deposition conditions, the material has good linearity and low detection limit for the detection of Cu2+ in the concentration range of 1-35 μg/L and Hg2+ in the concentration range of 5-40 μg/L. The limits of detection (LOD) were LOD(Cu) = 0.78 μg/L and LOD(Hg) = 0.19 μg/L for individual detection. When the two ions were detected at the same time, there was a good linearity for Cu2+, but the linear detection results for Hg2+ were partially disordered. In addition, the sensor exhibits good anti-interference and detection stability, showing the potential for practical applications.

A Novel Nickel(II) Porphyrin- Enhanced Glassy Carbon Electrode for High-Sensitivity Detection of Bisphenol A

Abstract Bisphenol A (BA), a widely used synthetic chemical in plastic production, is an endocrine-disrupting compound known to cause significant health and environmental harm. The urgent need for a simple and efficient technique to quantitatively monitor BA has led to the advancement of a novel electrochemical sensor. This sensor is based on nickel(II) meso-tetrakis(p-chlorophenyl)porphyrin [Ni(TClPP)]-modified glassy carbon electrode (GCE). Nickel porphyrin complexes show potential as electrochemical sensors due to their unique redox characteristics and structural features, enabling the detection of specific analytes in aqueous solutions. This capability positions them as valuable tools for environmental monitoring and analytical chemistry applications. To explore this potential further, we synthesized nickel(II) meso-tetrakis(p-chlorophenyl)porphyrin [Ni(TClPP)] and characterized it using UV-Vis, 1H NMR, and IR spectroscopy, as well as MALDI-TOF mass spectrometry. After drop-coating [Ni(TClPP)] onto the GCE, the sensor's performance was assessed via square wave voltammetry (SWV). It exhibited a linear response over an extensive concentration range (5×10-9M to 5×10-4M) with an exceptionally low detection limit of 5×10-9M. The [Ni(TClPP)]-GCE sensor demonstrated excellent selectivity and stability making it a strong candidate for BA detection in real sample.

Evaluation of circulating cytokine concentrations and ex vivo indicators of the inflammatory response in transition dairy cows fed pre- and postpartum diets differing in metabolizable protein supply.

The nutrient deficit during the transition period might alter activity of the nutrient sensing mechanistic target of rapamycin, thereby influencing immune phenotype and the inflammatory balance of transition cows. We investigated changes in circulating markers of inflammation during the transition period. Additionally, we assessed changes in ex-vivo indicators of the whole blood leukocyte cytokine response to LPS stimulation and leukocyte phagocytosis and oxidative burst. The second objective was to determine whether increasing the MP supply in the prepartum, the postpartum, or both diets would affect the measured parameters. Multiparous Holstein cows (n = 96) were assigned to 1 of 4 treatment groups at 28 d before expected calving following a randomized block design. Prepartum diets were formulated to contain either a control (85 g of MP/kg DM) or high (113 g of MP/kg DM) level of estimated MP. Postpartum diets were formulated to contain either a control (104 g of MP/kg DM) or high (131 g of MP/kg DM) level of estimated MP. To control the potential confounding effect of Met and Lys supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of ME in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and a postpartum diet resulted in treatment groups: control-control (CC), control-high (CH), high-control (HC), and high-high (HH). Serum concentrations of tumor necrosis factor (TNF), interleukin-10 (IL-10), and interferon-γ (IFN- γ) were determined at -6, 3, 10, and 21 d relative to calving using a multiplex assay. Complete blood cell count, whole blood cytokine response to LPS stimulation, and polymorphonuclear leukocyte (PMN) and peripheral blood mononuclear cell (PBMC) phagocytosis and oxidative burst were determined at -28, -10, 7, and 21 d relative to calving. Serum concentrations of TNF were below the lower limit of detection (≤12 pg/mL) in 282 (75.4%) samples. Serum concentrations of IL-10 and IFN-γ were greatest at -6 d relative to calving. Serum concentrations of IFN-γ did not differ by treatment, but IL-10 was greater in CH compared with HH and HC at 10 and 21 DIM, respectfully. Compared with CC, white blood cell counts were 13.9% higher in HC, granulocyte counts were 17.6 and 14.7% higher in CH and HC, respectively and monocyte counts were 27.4% higher at 7 DIM in HC. Lymphocyte counts were 12.7% and 13.9% higher in HC compared with CC and CH, respectively. Phagocytic ability and oxidative burst of PMN and PBMC did not differ by treatment. Whole blood LPS-induced IL-10 and TNF concentrations increased to a greater extent at 7 DIM and 7 and 21 DIM compared with -10 d relative to calving, respectively, and similarly in all treatments. In summary, while serum IL-10 and IFN-γ concentrations were greatest during late gestation, whole blood LPS-induced cytokines and phagocytosis increased to a greater extent during early lactation suggesting a robust inflammatory response. However, increasing the MP supply during the transition period did not meaningfully influence indicators of the inflammatory response.

Sensitive Ratiometric Luminescent FRET Probe for the Detection of Riboflavin.

The synthesis of two isomorphic 2D MOFs {[Ln(L)(NO3)(DMF)2] DMF} (Ln = Ho and Er, H2L = 2,5-bis(1,2,4-triazol-1-yl) terephthalic acid) by the solvothermal method enables ratio luminescent sensing of riboflavin (RF), based on the Förster resonance energy transfer (FRET) effect. As sensors for RF, both Ho-MOF and Er-MOF have splendid anti-interference effects, a large Stokes shift with 103 nm, excellent visualization effect, and a low detection limit, as low as 1.72 and 3.90 nM. Ho-MOF, with a better anti-interference capability and a relatively lower detection limit, is selected for further investigations. It possesses the advantages of excellent pH stability in the range of 4-12, rapid response time within 50 s, and even achieving five cycles. Ho-MOF also demonstrates exceptional practical detection potential when tested in real-life environments and samples, with urine and serum exhibiting detection limits of 5.26 and 27.27 nM, respectively, and a recovery range of 96-104% in VB2 tablets. Mechanism research discovers that FRET serves as the primary sensing mechanism with a calculated Forster distance (R0) of 3.7 nm, which is consistent with the required distance (1-10 nm). This study successfully achieves rate-luminescent sensing and monitoring of RF in diverse environments.

Large Area and Flexible Flexion Sensing Matrix for Detection of Strain Distribution in Bendable and Curved Surface.

Flexible flexion sensors are attracting attention due to their wide range of applications. It is urgent to develop a flexible sensor matrix to detect strain distribution on curved surfaces for object surface posture reconstruction, fault detection, and predictive maintenance. Herein, a convenient and universal method for preparing a flexible flexion sensor matrix is proposed using a versatile screen-printing technique. Compared to traditional thin film configurations, this process improved the sensitivity by introducing multiple interfaces and can be used for the fabrication of large-area flexion sensor matrix with high stability and consistency. The prepared flexible flexion sensors performed with a low detection limit (0.07%), a remarkable gauge factor (>50), and high stability (no apparent decay after 2000 bending-releasing cycles). We also demonstrated their applications in monitoring human body movement and gesture recognition. The sensors were integrated into a data glove for real-time robotic arm control, and achieved an accuracy rate of over 96% in recognizing various gestures with a neural network model. A large area flexible flexion sensor matrix (8 × 8) was fabricated by full-printing technique and enables simultaneous monitoring of multiposition bending states, which has significant potential in real-time tracking the strain distribution in bendable and curved surfaces.

Green Fabrication of Sulfonium-Containing Bismuth Materials for High-Sensitivity X-Ray Detection.

Organic-inorganic hybrid materials based on lead and bismuth have recently been proposed as novel X- and gamma-ray detectors for medical imaging, non-destructive testing, and security, due to their high atomic numbers and facile preparation compared to traditional materials like amorphous selenium and Cd(Zn)Te. However, challenges related to device operation, excessively high dark currents, and long-term stability have delayed commercialization. Here, two novel semiconductors incorporating stable sulfonium cations are presented, [(CH3CH2)3S]6Bi8I30 and [(CH3CH2)3S]AgBiI5, synthesized via solvent-free ball milling and fabricated into dense polycrystalline pellets using cold isostatic compression, two techniques that can easily be upscaled, for X-ray detection application. The fabricated detectors exhibit exceptional sensitivities (14100-15190µCGyair -1cm-2) and low detection limits (90nGyairs-1 for [(CH3CH2)3S]6Bi8I30 and 78nGyairs-1 for [(CH3CH2)3S]AgBiI5), far surpassing current commercial detectors. Notably, they maintain performance after 9 months of ambient storage. The findings highlight [(CH3CH2)3S]6Bi8I30 and [(CH3CH2)3S]AgBiI5 as scalable, cost-effective and highly stable alternatives to traditional semiconductor materials, offering great potential as X-ray detectors in medical and security applications.

High-sensitivity detection of tetracycline using phosphorus-doped carbon quantum dots prepared by pyrolysis method as fluorescent probes

Abstract The selective and highly sensitive detection of trace tetracycline antibiotic residues is crucial for ensuring food safety and maintaining organismal health. In the present study, we describe a novel method for tetracycline detection utilizing phosphorus-doped carbon quantum dots (P-CQDs) synthesized via solid-phase pyrolysis as fluorescent probes. Phosphorus doping significantly amplifies the fluorescence intensity by a factor of 8.1, and the resulting P-CQDs exhibit superior optical stability. The excitation and emission maxima of the P-CQDs are located at 340 nm and 440 nm, respectively. The fluorescent probe detects tetracycline based on the inner filter effect, demonstrating high selectivity and strong interference resistance. It has a wide detection range of 0–80 μM and a low detection limit of 0.120 μM. This method has been effectively applied to the analysis of real samples, yielding satisfactory results.