Nanomolar Detection Limit Research Articles

Activity-Based Dicyanoisophorone Derivatives: Fluorogenic Toolbox Enables Direct Visualization and Monitoring of Esterase Activity in Tumor Models.

The visualization and spatiotemporal monitoring of endogenous esterase activity are crucial for clinical diagnostics and treatment of liver diseases. Our research adopts a novel substrate hydrolysis-enzymatic activity (SHEA) approach using dicyanoisophorone-based fluorogenic ester substrates DCIP-R (R = R1-R6) to evaluate esterase preferences on diverse substrate libraries. Esterase-mediated hydrolysis yielded fluorescent DCIP-OH with a nanomolar detection limit in vitro. These probes effectively monitor ester hydrolysis kinetics with a turnover number of 4.73 s-1 and catalytic efficiency (kcat/Km) of 106 M-1 s-1 (DCIP-R1). Comparative studies utilizing two-photon imaging have indicated that substrates containing alkyl groups (DCIP-R1) as recognition elements exhibit enhanced enzymatic cleavage compared to those containing phenyl substitution on alkyl chains (DCIP-R4). Time-dependent variations in endogenous esterase levels were tracked in healthy and liver tumor models, especially in diethylnitrosamine (DEN)-induced tumors and HepG2-transplanted liver tumors. Overall, fluorescence signal quantifications demonstrated the excellent proficiency of DCIP-R1 in detecting esterase activity both in vitro and in vivo, showing promising potential for biomedical applications.

8-Anilino-1-naphthalenesulfonate-Conjugated Carbon-Coated Ferrite Nanodots for Fluoromagnetic Imaging, Smart Drug Delivery, and Biomolecular Sensing

Background: Superparamagnetic properties and excitation independence have been incorporated into carbon-decorated manganese ferrite nanodots (MnFe@C) to introduce an economical and safer multimodal agent for use in both T1-T2 MRI and fluorescence-based imaging to replace the conventional highly toxic heavy metal contrast agents. Methods: The surface conjugation of 8-anilino-1-naphthalenesulfonate (ANS) to MnFe@C nanodots (ANS-MnFe@C) enhances both longitudinal and transverse MRI relaxation, improves fluorescence for optical imaging, and increases protein detection sensitivity, showing higher multimodal efficacy in terms of molar relaxivity, radiant efficiencies, and fluorescence sensitivity compared to MnFe@C. Results: The band gap energy was determined using Tauc’s equation to be 3.32 eV, while a 72% quantum yield demonstrated that ANS-MnFe@C was highly fluorescent, with the linear range and association constant calculated using the Stern–Volmer relation. The synthesized ANS-MnFe@C demonstrated excellent selectivity and sensitivity for bovine serum albumin (BSA), with a nanomolar detection limit of 367.09 nM and a broad linear range from 0.015 to 0.225 mM. Conclusions: In conclusion, ANS-MnFe@C holds ease of fabrication, good biocompatibility, as assessed in A375 cells, and an effective pH-sensitive doxorubicin release profile to establish anticancer activity in lung cancer cell line (A549), highlighting its potential as an affordable therapeutic agent for multimodal imaging, drug delivery, and protein sensing.

Aptamer-Mediated Electrochemical Detection of SARS-CoV-2 Nucleocapsid Protein in Saliva.

Gold standard detection of SARS-CoV-2 by reverse transcription quantitative PCR (RT-qPCR) can achieve ultrasensitive viral detection down to a few RNA copies per sample. Yet, the lengthy detection and labor-intensive protocol limit its effectiveness in community screening. In view of this, a structural switching electrochemical aptamer-based biosensor (E-AB) targeting the SARS-CoV-2 nucleocapsid (N) protein was developed. Four N protein-targeting aptamers were characterized on an electrochemical cell configuration using square wave voltammetry (SWV). The sensor was investigated in an artificial saliva matrix optimizing the aptamer anchoring orientation, SWV interrogation frequency, and target incubation time. Rapid detection of the N protein was achieved within 5 min at a low nanomolar limit of detection (LOD) with high specificity. Specific N protein detection was also achieved in simulated positive saliva samples, demonstrating its feasibility for saliva-based rapid diagnosis. Further research will incorporate novel signal amplification strategies to improve sensitivity for early diagnosis.

Customizable OpenGUS immunoassay: A homogeneous detection system using β-glucuronidase switch and label-free antibody

We developed a customizable OpenGUS immunoassay that enables rapid and sensitive detection of analytes without requiring antibody modification. This immunoassay employs label-free whole antibodies, an antibody-binding Z domain (ZD) derived from Staphylococcal protein A, and a β-glucuronidase (GUS) switch mutant, allowing for easy replacement of antibodies to tailor the immunoassays for various targeted antigens. The working principle is that the OpenGUS probe, the fusion protein of ZD and a GUS switch, converts the antibody-antigen interaction into GUS activation in a one-pot reaction. To enhance the signal-to-background ratio of the immunoassay, a GUS switch mutant that exhibits reduced background activation was developed by screening several additional mutations at the diagonal interface residue H514. Moreover, we optimized the composition of the reaction buffer, including organic solvents, salt, and surfactant. Under optimal conditions, we customized OpenGUS immunoassays for Cry j 1, human C-reactive protein, and human lactoferrin, achieving around 10–20-fold maximum fluorescence (15 min) or colorimetric (2 h) responses with picomolar to low nanomolar level detection limit, simply by using commercially available IgGs. Additionally, the three analytes were successfully detected in complex matrices similar to those used in practical applications. We believe that this customizable OpenGUS immunoassay will pave the way for the prompt development of rapid and sensitive homogeneous immunoassays for point-of-care diagnostics, high-throughput testing, and onsite environmental assessments.

A cost-effective method for the sensitive detection of levofloxacin using a 3D composite electrode composed of nail polish, graphite and aluminium oxide.

The potential impact on human health and the environment has spurred significant interest in detecting and quantifying pharmaceutical compounds across various matrices, from environmental to biological samples. Here, we present an electrochemical approach for determining levofloxacin in drug, synthetic urine, water, and breast milk samples. An affordable sensor was constructed using 3D printing and composite material based on nail polish, graphite, and aluminum oxide. The conductive composite material was characterized spectroscopically, electrochemically, and by imaging techniques. Subsequently, an electrochemical method based on square wave voltammetry was optimized and applied. The method exhibited good sensitivity (5.11 ± 0.0912 μA L μmol-1 cm-2) and enhanced stability (RSD = 7.2%), with electrochemical responses correlating with the concentration of levofloxacin in the samples tested, yielding recovery values in the range of 98 to 111%. The developed method demonstrated a robust linear working range from 2 to 100 μmol L-1 and a nanomolar detection limit of 128 nmol L-1, rendering it suitable for quantitative analysis. The sensor also shows promise as a platform for the sensitive detection of pharmaceutical compounds, contributing to greater safety and sustainability in these domains.

De-wetted gold nanostructures for SERS-based sensing of static and dynamic targets

De-wetting of metal thin film is one of the simplest fabrication techniques to produce metallic nanostructures for Surface-Enhanced Raman Spectroscopy (SERS)-based sensing. In this manuscript, we explore the sensitivity of a de-wetted metal SERS substrate by testing it with the organic dye Rhodamine 6G (R6G) as well as with the single amino acids (Glycine, Serine, and Histidine) and a binary mixture of Glycine and Serine mixture. We observe that repeated de-wetting of the metal thin film provides a more than ten times higher SERS enhancement factor compared to a single de-wetting. This is attributed to the presence of more closely spaced metal nanoclusters, enabling a higher electromagnetic field enhancement at the hotspots. We characterized the sensing capability of our SERS substrates by detecting R6G dye drop-casted onto the substrates at sub-femtomolar concentrations. We were also able to detect R6G in a dynamic state while it was transported across a 500 nm diameter pore with a nanomolar detection limit. Finally, we were also able to detect amino acids with a micromolar detection limit using our SERS substrate. These results indicate the promise in the integration of our SERS substrate with solid-state nanopores for SERS-based signal readout where concentrations higher than nanomolar exist in the pore due to high confinement.

Selective Chromo-Fluorogenic Chemoprobe for nM Al3+ Recognition: Experimental and Living-Cell Applications.

A rhodamine based chemoprobe BESN was engineered and employed as a selective ''OFF-ON'' chromo-fluorogenic sensor for Al3+ in H2O:MeOH (1:9, v:v). Notable changes in the absorption and emission spectra of BESN were clearly detectable upon the addition of Al3+. Sensitivity and binding mechanism studies demonstrated a good sensing performance of BESN with nanomolar detection limit (130nM), and it was found to be highly selective towards interfering metal ions. Besides, the binding constant between BESN and Al3+ was found to be 3.19 × 103M-1. Then, the validation study of BESN for Al3+ was performed based on significant analytical parameters and statistical tests. The binding of Al3+ with BESN (1:1) was probed via infrared, high-resolution mass and emission (Job's plot) spectroscopy measurements. The sensing performance of BESN could make it ideal chemosensor for real applications including vegetable, tuna fish and water samples, also for Smartphone and test-kit applications. The recovery values of the BESN to Al3+ were estimated within a range from 95.13% to 105.30% for water, 94.63% to 109.62% for tuna fish and 94.80% to 109.80% for vegetable samples. Additionally, the BESN has very low cytotoxicity and was triumphantly utilized for the recognition of Al3+ in living-cells.

Rapid Single Step Atmospheric Pressure Plasma Jet Deposition of a SERS Active Surface

Surface-enhanced Raman Spectroscopy (SERS) is a highly sensitive detection technique capable of nanomolar or lower detection limits for some analytes.1-3 The key parameter is control of the surface nanostructure to optimise this remarkable enhancement, providing non-destructive detection without the need for chemical labelling. The bottleneck for the wide applicability of SERS as a valuable analytical tool is twofold: (1) rapid fabrication with the required nanostructure and (2) the difficulty in recovering a baseline before exposure or re-exposure to the target matrix. Here we describe an atmospheric plasma jet method for rapid single-step synthesis of SERS active silver on glass and demonstrate the potential of plasma to remove the adsorbed analyte to recover a baseline.The method described in this study employs an atmospheric pressure plasma jet (APPJ) for rapid single-step deposition of nanostructured silver materials with SERS.4,5 Non-thermal plasmas under reduced pressure offer a unique redox chemistry, partly due to the highly energised electrons and are essential for processing many materials and chemical transformations. Electrochemically, a helium-conducting gas allows various redox reactions to occur, without the need of restricting solvent mediums. An APPJ presents a medium which can be considered an electrode due to the presence of electrons and electrolytes, with the ability to drive reduction processes.6 APPJs allow fascinating chemistry to occur, balancing the thermal kinetic energy distribution between electrons and other neutral and ionised species. Consequently, plasma jets are used for etching, cleaning, and medical treatments, as well as driving highly energised electrons in redox reactions.7-9 The plasma was ignited at a stainless-steel needle electrode tip positioned in a 440 mM I.D. ceramic nozzle, with a plume extending 2 mm from the nozzle tip. Silver deposits were ‘written’ precisely in a 2D regular pattern of plasma deposited silver on borosilicate glass for Raman interrogation without any post-treatment by feeding a silver salt into the APPJ. The APPJ ceramic nozzle prints 125 ± 25 m diameter silver islands with a height of approx. 370 nm, separated by 500 mm, these islands formed the rudimentary SERS substrates.The surface morphology and microstructure through SEM and AFM will be described– assessing how microstructure will correlate to SERS enhancement. The concentration dependence will be quantitatively evaluated using various analytes over a wide range of 1 x 10-7 M to 1 x 10-2 M. The detection limit was calculated using three times the lowest concentration detectable standard deviation, equating to 154 ppb. The particle morphology and SERS enhancement are compared to various commercial substrates. Using the same APPJ system for the deposition of silver metal, a helium plasma doped with 4 % oxygen, followed by a separate treatment of helium doped with 4 % hydrogen, was found effective in restoring the zero baseline Raman response. After the cleaning steps, all analytes could show zero baseline recovery with Raman response regeneration. After successive cycles of application of analyte and then oxygen and hydrogen treatment, there is a slight drop in the SERS signal.4,10 Silver readily oxidises to form silver oxide after exposure to helium plasma doped with oxygen, as confirmed using XRD and XPS. This plasma oxidation causes a change in the microstructure of the particles, ultimately sintering together with successive oxidation cycles.Plasma-prepared substrates show significant gains with respect to the economical use of materials and the rapidity of the synthesis of the substrates. We showcase using the atmospheric pressure plasma jet method for synthesis and baseline recovery as an integral part of an analytical device. This approach presents the prospect of reusing the same SERS device for analysis, which may be a key advantage for academic and industrial applications. 11-13 Figure caption:(a) Raman spectra of R6G with most prominent peak measured at 1651cm-1 after oxygen and hydrogen treatment with the black lines showing the Raman spectra of the surface before application of analyte. (b) The peak intensity at 1586cm-1 peak for 4MBA for each measurement cycle with the analyte and before analyte application (after oxygen and hydrogen treatment) (c) Depicting the cleaning and regeneration of SERS signal on a borosilicate substrate. Both 4MBA and R6G were dissolved in methanol at 1 x 10-4M and drop cast onto the substrate. (d) normal X-ray diffraction spectra of PDS between 5 – 80 o 2θ for the original plasma deposit (i), oxidised plasma clean (ii) and hydrogen plasma clean (iii). All assignment was carried out using the Bruker XRD database, using JCPDS 04-0783 and 43-0997 for Ag and Ag2O, respectively. Figure 1

Rationalizing Diverse Binding Mechanisms to the Same Protein Fold: Insights for Ligand Recognition and Biosensor Design.

The engineering of novel protein-ligand binding interactions, particularly for complex drug-like molecules, is an unsolved problem, which could enable many practical applications of protein biosensors. In this work, we analyzed two engineered biosensors, derived from the plant hormone sensor PYR1, to recognize either the agrochemical mandipropamid or the synthetic cannabinoid WIN55,212-2. Using a combination of quantitative deep mutational scanning experiments and molecular dynamics simulations, we demonstrated that mutations at common positions can promote protein-ligand shape complementarity and revealed prominent differences in the electrostatic networks needed to complement diverse ligands. MD simulations indicate that both PYR1 protein-ligand complexes bind a single conformer of their target ligand that is close to the lowest free-energy conformer. Computational design using a fixed conformer and rigid body orientation led to new WIN55,212-2 sensors with nanomolar limits of detection. This work reveals mechanisms by which the versatile PYR1 biosensor scaffold can bind diverse ligands. This work also provides computational methods to sample realistic ligand conformers and rigid body alignments that simplify the computational design of biosensors for novel ligands of interest.

Engineering FeOOH/Fe2O3@Carbon Interfaces With Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27 °C and 120 °C, Fe5H9O15/Fe2O3@sp2-carbon transforms into β-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The β-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, β-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the β-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

Fast and scalable fabrication of Ag/TiO2 nanostructured substrates for enhanced plasmonic sensing and photocatalytic applications

Here we propose a fast and scalable (up to 3 min for 6 × 1 cm size substrate) innovative approach to fabricate coral-shaped TiO2 nanostructured substrates based on thermal oxidation of titanium foil followed by deposition of Ag nanoparticles for bifunctional sensing and photocatalysis. Comprehensive studies on the morphology, crystal structure, stoichiometry, optical, and electronic properties of these nanostructures reveal the formation of a Schottky barrier at the Ag/TiO2 interface. This interface alters the electronic structure of the Ag/TiO2 nanosystem, retaining the plasmonic properties of Ag nanoparticles while enhancing their catalytic activity. The SERS performance and photocatalytic activity of Ag/TiO2 nanostructures are demonstrated by the test analyte Rhodamine 6G detection down to concentrations of 10-12 M and acceleration of its degradation under simulated sunlight by 5.8 times. Tests with tetracycline water solutions indicate a nanomolar detection limit and 4.4-fold increase in degradation rate. The proposed Ag/TiO2 nanostructures are prospective for creation of low-cost bifunctional platforms for the sensitive detection of organic residues in water as well as their fast neutralization under solar light.

Synthesis and characterization of a xanthene-based molecular probe to detect triphosgene in solution and vapor phases

The ability of a detection approach to direct a visible and easy-to-monitor characteristic is an important aspect of molecular-level detection. From this viewpoint, we developed the molecular probe Xanth-Py, which allows us to visually detect triphosgene (TPG) by modulating the probe's photophysical characteristics. Since Xanth-Py exhibits a strong fluorescence, its interaction with TPG causes the non-radiative decay of the probe. As TPG concentrations increase, the fluorescence intensity decreases linearly, leading to a nanomolar level detection limit. The interaction of Xanth-Py with TPG accompanied a color change from pink to blue, enabling a visible detection protocol. Probe-coated paper strips have been used as an inexpensive detection tool for vapor-phase TPG detection, revealing the potential of the Xanth-Py. Further, triphosgene has been detected using a smartphone-assisted RGB analysis tool in conjunction with a portable UV-light source device.

Ultrasonically Assembled 0-D Zirconium Oxide on TiO2 Nanorod for a Sensitive Determination of Antibiotic Drug in Biological Samples

Biological, food, and water samples were used to determine the amount of Furazolidone (FUZ) in a variety of applications, including health and nutrition, diagnosis/treatment, pharmacological research, and food/drug quality monitoring. Using hydrothermal and ultrasonication strategies, new type of TiO2 (1D) and ZrO2 (0D) (TiO2/ZrO2) nanocomposites were prepared for FUZ determination. Then the prepared nanocomposite was characterization under X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultra violet visible spectroscopy, and the electrochemical property of the material was characterized by electrochemical impedance spectroscopy and cyclic voltammetry (CV). In addition, detection of FUZ was analyzed by electroanalytical studies such as CV and differential pulse voltammetry (DPV). This proposed TiO2/ZrO2/GCE sensor exhibits excellent electrochemical characteristics, including excellent linearity (0.01–537.22 μM), nanomolar detection limit (19 nM), and encouraging sensitivity (0.35 μA μM−1cm−2) and it shows greater selectivity, repeatability, and longer storage stability. Along with concerned realizability, the primed sensor was analyzed over biological samples that reveal good recovery in real samples.

Reversible NIR emitting fluorescent sensor with biocompatible and large Stokes shift for the Zn2+ in environmental samples and living cells

Herein, a simple dicyanoisophoron-based near-infrared (NIR) fluorescent sensorIQhas beendesigned and constructed for the rapid recognition of Zn2+in environmental samples and living systems. The synthesized NIR sensorIQin H2O/EtOH/ (1/9, v/v) displayed excellent recognition performances towards Zn2+including nano-molar detection limit (60.5 nM)and a large Stokes shift (173 nm). SensorIQwas successively applied to realize the determination of Zn2+in smartphone applications.Furthermore,IQ-loaded test strips, cotton swabs, and polysulfone capsules were able to quickly determine the presence of Zn2+. Besides,IQwas effectively employed to monitor Zn2+content in actual environmental samples (tap, pure, and lake water samples, rice, and potato). Additionally, the imaging potential ofIQwas utilized to visualize Zn2+in living cells. The results from these applications indicated that the designed probeIQis hopeful to be utilized for the recognition of Zn2+in multiple applications.

Water-Soluble Triazolium Covalent Cages for ATP Sensing.

Water-soluble organic cages are attractive targets for their molecular recognition and sensing features of biologically relevant molecules. Here, we have successfully designed and synthesized a pair of water-soluble cationic cages employing click reaction as the fundamental step followed by the N-methylation of the triazole rings. The rigid and shape-persistent 3D hydrophobic cavity, positively charged surface, H-bonding triazolium rings, and excellent water solubility empower both cages to exhibit a superior affinity and selectivity for binding with adenosine-5'-triphosphate (ATP) compared to cyclophanes and other macrocyclic receptors. Both cage molecules (PCC⋅Cl and BCC⋅Cl) can bind a highly emissive dye HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt) to form non-fluorescent complexes. The addition of ATP resulted in the stronger cage⊂ATP complexes with the retention of HPTS emission upon its displacement. The resultant indicator-displacement assay system can efficiently sense and quantify ATP in nanomolar detection limits in buffer solutions and human serum matrix. Spectroscopic and theoretical studies revealed the synergistic effect of π⋅⋅⋅π stacking interaction between the aromatic moiety of the cationic cages and the adenine moiety of ATP, as well as the electrostatic and hydrogen bonding interaction between the phosphate anion of ATP and triazole protons of cages, played the pivotal roles in the sensing process.

Thiolated Chiral Naphthalene Diimide Derivatives as Effective Selectors of the β‐Blocker Atenolol Enantiomers

AbstractAtenolol β‐blocker drug (ATN) to treat hypertension and cardiovascular disorders such as angina pectoris is manufactured commercially in a racemic form, while only its (S)‐enantiomer shows selective β1‐blocking activity. Here, a new axially chiral thiolated naphthalene diimide derivatives (HS‐BIN‐NDI) for the rapid, simple, and sensitive detection of ATN enantiomers is presented. The Surface Plasmon Resonance (SPR) and Atomic Force Microscopy (AFM) experiments show that interactions between a chiral selector and a chiral analyte occur only when their configurations are opposite. The extensive computational simulations support this finding. The association coefficient determined by SPR is high (105‐106 M−1 s−1) and indicates that the interactions are electrostatic. The analytical utility of atropisomeric HS‐BIN‐NDIs is proven, and the voltammetric sensors designed to determine ATN enantiomers are constructed. The developed sensors are characterized by a wide analytical operating range from 5.0·10−3 to 1.0 µm, nanomolar detection limit, high selectivity, and a long lifetime. Several additives like urea, creatinine, glucose, human albumin, and hemoglobin do not affect ATN sensing.

Binary metal oxide (NiO/SnO2) composite with electrochemical bifunction: Detection of neuro transmitting drug and catalysis for hydrogen evolution reaction

The synergetic effect between dual oxides in binary metal oxides (BMO) makes them promising electrode materials for the detection of toxic chemicals, and biological compounds. In addition, the interaction between the cations and anions of diverse metals in BMO tends to create more oxygen vacancies which are beneficial for energy storage devices. However, specifically targeted synthesis of BMO is still arduous. In this work, we prepared a nickel oxide/tin oxide composite (NiO/SnO2) through a simple solvothermal technique. The crystallinity, specific surface area, and morphology were fully characterized. The synthesized BMO is used as a bifunctional electrocatalyst for the electrochemical detection of dopamine (DPA) and for the hydrogen evolution reaction (HER). As expected, the active metals in the NiO/SnO2 composite afforded a higher redox current at a reduced redox potential with a nanomolar level detection limit (4 nm) and excellent selectivity. Moreover, a better recovery rate is achieved in the real-time detection of DPA in human urine and DPA injection solution. Compared to other metal oxides, NiO/SnO2 composite afforded lower overpotential (157 mV @10 mA cm−2), Tafel slope (155 mV dec−1), and long-term durability, with a minimum retention rate. These studies conclude that NiO/SnO2 composite can act as a suitable electrode modifier for electrochemical sensing and the HER.

Atomic layer deposition-fabricated two-dimensional MoO3-WO3 nanohybrid thin-film electrode for ultrasensitive and interference-free detection of dopamine

Atomically thin two-dimensional (2D) semiconductors and their hybrid electrodes show great promise in the advancement of neural sensors for detecting neurotransmitters either through implantation on the brain's surface or by direct detection in biological fluids. This research demonstrated the fabrication of a sub-10 nm thick 2D MoO3-WO3 heterostructure electrode via atomic layer deposition (ALD) for the first time to detect dopamine (DA). The developed thin-film with uniform surface morphology possessed monoclinic and orthorhombic crystal structures of WO3 and MoO3, respectively, with the presence of oxygen vacancies and their sub-stoichiometric phases. The MoO3-WO3 sensor showed excellent catalytic activity for the interference-free detection of DA by suppressing the redox activity of common interferences, ascorbic acid (AA) and uric acid (UA). The ultra-sensitivity of DA oxidation can be ascribed to the effective electrostatic interaction and chemical coordination between the positively charged DA (at pH 7.0) and the MoO3-WO3. In contrast, the predominant electrostatic repulsive force between the negatively charged AA and UA (at pH 7.0) and the MoO3-WO3 suppressed their electrochemical responses. The sensor showed a nanomolar detection limit (20 nM) and a wide linear range for DA detection, which is highly appropriate for its determination in biological samples. Additionally, the sensor demonstrated excellent electrochemical stability, high reproducibility, and good recoveries of DA determination in diluted human serum samples.

Nanomolar level colorimetric and On–Off fluorimetric sensing of Cu2+: Theoretical, Smartphone, test kit and food application outcomes

A novel naphthaldehyde–based colorimetric and fluorogenic molecular sensor PHNAP [(E)–1–(((4–(phenylamino)phenyl)imino)methyl)naphthalen–2–ol] was developed for the recognition of Cu2+ with outstanding selectivity. After treatment with Cu2+, the PHNAP showed remarkable color transforms from ''yellow'' to ''colorless'' under UV–cabin and ''yellow'' to ''pink'' under daylight. Under the optimum sensing conditions, Cu2+ was selectively recognized and sensitively determined with a nanomolar detection limit (6.61 nM; 3σ/K). The PHNAP showed very fast and Cys-reversible response for Cu2+. The Job's plot and TOF–MS data were gathered to authenticate the mechanism of the binding. The DFT calculations also confirmed the proposed sensing phenomenon. Furthermore, PHNAP–based portable test kits were simply fabricated for the visual recognition of Cu2+. The PHNAP was used in diverse samples for the quantitatively recognition of Cu2+; likewise, the smartphone appliance was successfully performed without the aid of any sophisticated tool and the outstanding visual response of PHNAP.

Fluorescent Switch-on Detection of Cadmium(II) Using Salicylaldehyde-Decorated Gold Nanoclusters.

In this study, salicylaldehyde (SA) conjugated gold nanoclusters were synthesized, characterized, and applied for the fluorescent turn-on sensing of Cd2+. The trypsin-stabilized fluorescent gold nanocluster (Tryp-AuNCs, λem = 680nm) was modified with SA to form the spherical-shaped SA_Tryp-AuNCs. After modification, the red-emitting Tryp-AuNCs turned to green-emitting SA_Tryp-AuNCs because of the formation of imine linkage between the -CHO group of SA with the -NH2 group of functionalized trypsin. The modified SA_Tryp-AuNCs selectively interacted with Cd2+ and exhibited a fluorescence enhancement at 660nm. The Cd2+ detection with SA_Tryp-AuNCs is simple and rapid with an estimated nanomolar detection limit of 98.1 nM. The practical utility of SA_Tryp-AuNCs was validated by quantifying Cd2+ in real environmental water samples.