Superior Detection Limit Research Articles

Nano-Needle Boron-Doped Diamond Film with High Electrochemical Performance of Detecting Lead Ions

Nano-needle boron-doped diamond (NNBDD) films increase their performance when used as electrodes in the determination of Pb2+. We develop a simple and economical route to produce NNBDD based on the investigation of the diamond growth mode and the ratio of diamond to non-diamond carbon without involving any templates. An enhancement in surface area is achievable for NNBDD film. The NNBDD electrodes are characterized through scanning electron microscopy, Raman spectroscopy, X-ray diffraction, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse anodic stripping voltammetry (DPASV). Furthermore, we use a finite-element numerical method to research the prospects of tip-enhanced electric fields for sensitive detection at low Pb2+ concentrations. The NNBDD exhibits significant advantages and great electrical conductivity and is applied to detect trace Pb2+ through DPASV. Under pre-deposition accumulation conditions, a wide linear range from 1 to 80 µgL−1 is achieved. A superior detection limit of 0.32 µgL−1 is achieved for Pb2+, which indicates great potential for the sensitive detection of heavy metal ions.

Low-cost colorimetric mercury sensor based on immobilisation of rhodamine B thiolactone in a sustainable agar-agar gel substrate

The global impact of mercury (Hg) pollution requires the development of improved low-cost analytical sensors for Hg determination. Rhodamine B thiolactone (RBT) has been proposed as a colorimetric sensor for Hg2+ as it undergoes ring-opening in the presence of Hg to give a fast, reliable, and easily observed, colour change. In this study a naked-eye biopolymer-based sensor for Hg2+ detection was developed based on RBT-doped agar-agar membranes supported on filter papers. The chromogenic reagent was stable at −18 °C for over two years, whilst the RBT-doped sol–gel membranes prepared from 1% (w/v) agar colloid had a shelf-life of at least 12 weeks at room temperature when stored in the dark. The limit of detection (LOD) for naked-eye sensing was 0.4 μg L−1. For Hg2+ quantification, images of the membranes were recorded using a flatbed scanner and analysed with public-domain ImageJ software. The linear range based on greyscale intensity in the green channel was 0.2–6.0 μg L−1 and the LOD was 0.2 µg L−1. Precision was 10% (n = 3) and spike recoveries were in the range 97–103%. The sensors were regenerated using 10% w/v KI and successfully reused up to 4 times. Compared with other RBT-doped sol–gel sensors, the agar-agar membranes were simpler to prepare, more environmentally friendly, and gave a superior detection limit.

Real-Time Detection and Speciation of Mn Dissolution in a Li-Ion Battery Cathode

Rechargeable lithium-ion batteries (LIB) are widely used in portable electronic devices, electric vehicles, medical devices, etc. thanks to their improved performance in recent decades. The properties of the cathode still largely limit the overall performance, as the cathode usually has lower theoretical capacity and suffers from more serious degradation effects.1 Among these, dissolution of transition metals is an important but poorly understood side reaction. On the one hand, it dominates the cathode capacity fading by causing irreversible loss of active redox sites, phase transformation, cation mixing, grain fracture, etc. On the other hand, the dissolved transition metal ions can exacerbate the formation of the solid electrolyte interphase (SEI) on the anode through a dissolution-migration-deposition (DMD) process.2 Here, we focus on the dissolution of manganese from LiMn2O4 (LMO), a benchmark cathode material, through real-time analysis of the electrolyte by combining online inductively coupled plasma–optical emission spectroscopy (online ICP-OES) and rotating ring-disc electrode (RRDE) collection, Figure 1. Both methods offer real-time dissolution information as functions of time and potential/state of charge, while the former shows superior detection limits and the latter provides oxidation state information of the dissolving species.According to online ICP-OES, we find that Mn dissolves readily from fully lithiated LMO when brought in contact with aqueous 0.2 M Li2SO4, but that a dissolution-passivation process stops further detectable dissolution until well past fully delithiated λ-MnO2. The dissolution becomes detectable again on the returning scan to the potential of pristine LMO, and grows exponentially in the overlithiated region.3 Our RRDE results indicate that Mn2+ is the dominating dissolved Mn species only in overlithiation region, whereas it only accounts for a minor proportion in the dissolved species from delithiation region. The data from both techniques suggest that the dissolution of Mn is related to the surface state of the electrode, rather than its degree of lithiation, as widely believed in the past.4 Our results provide a better understanding of the mechanism of transition metal dissolution in cathode materials, as well as an entry point for screening next-generation cathodes and metal ion batteries with superior degradation characteristics.5

Multifunctional Roles of Dihydrotetrazine-Decorated Zr-MOFs in Photoluminescence and Colorimetrism for Discrimination of Arsenate and Phosphate Ions in Water.

The high chemical and structural stabilities of zirconium (Zr)-based metal-organic frameworks (MOFs) in aquatic media make them ideal candidates for wastewater treatment. Rational decoration or Zr-MOFs with functional groups can significantly extend their application in this area. In this work, two well-known Zr-MOFs, UiO-66 and MIL-140-A, were functionalized with dihydrotetrazine function to increase their capability in water treatment. Investigations reveal that these two dihydrotetrazine (DHTZ)-functionalized MOFs, namely UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, can be applied as a two-component array for highly selective and sensitive discrimination of arsenate (AsO43-) and phosphate (PO43-) ions in water in the presence of other anions. Photoluminescence (PL) tests using UiO-66(Zr)-DHTZ show that this MOF can detect these two anions via a ratiometric response, 1.74 for arsenate and 1.84 for phosphate at 2 μM, with superior detection limits (7.2 × 10-8 M for AsO43- and 4.3 × 10-8 M for PO43-). The ratiometric PL response of UiO-66(Zr)-DHTZ toward arsenate and phosphate anions arises possibly from the arsenate-dihydrotetrazine hydrogen bonding. In the next step, colorimetric tests using MIL-140(Zr)-DHTZ were conducted to discriminate the arsenate from phosphate with a very low detection limit at nanomolar level. This MOF undergoes a yellow-to-pink color change in the presence of arsenate ions, while no color change is observed in the presence of phosphate. This color change is observed through conversion of dihydrotetrazine sites inside the pores of MIL-140(Zr)-DHTZ into tetrazine. Altogether, the PL response of UiO-66(Zr)-DHTZ is originated from the hydrogen bond-donating/accepting character of DHTZ function, while the colorimetric response of MIL-140(Zr)-DHTZ is based on the chemical conversion of DHTZ function. This work clearly shows that the decoration of Zr-based MOFs with multicharacter functional groups can develop their application in wastewater treatment as multipurpose platforms.

Biomimetic sandwich assay of proteins with a photoelectrochemical sensor using molecularly imprinted targeting and self-ratiometric signaling

A novel photoelectrochemical (PEC) sensor based on dual-molecularly imprinted polymer (MIP) and self-ratiometric strategy was developed for measuring disease marker. The human papillomavirus 16 (HPV16) L1 protein was selected as a target model. The sensing elements contain TiO2 @Au as the PEC material, the MIP film as the primary artificial recognizer, and the alkaline phosphatase-labelled MIP nanoparticles (ALP-nanoMIPs) as the secondary artificial recognizer. Both MIPs were fabricated with a tailored and controllable process using merely a tiny epitope of the target protein as the templates. With the addition of L1 protein, a sandwich structure was formed and based on the dual-MIPs recognition. Ascorbic acid as the electron donor was produced and promoted the transient photocurrent response. Meanwhile, the steady photocurrent response decreased, arising from hinderance effect of the target protein rebinding for MIP film. This MIP sensor exhibited superior limit of detection (∼0.1 pg mL−1) and a broad linear range (0.28 pg mL−1 to 28 ng mL−1) for L1 protein. Good performance in terms of robustness, stability, selectivity, and repeatability was also confirmed. The designed MIP sensor has significant potential in extensive fields of low-cost antigen marker tests and healthcare screening.

Highly Efficient Wavelength-Resolved Electrochemiluminescence of Carbon Nitride Films for Ultrasensitive Multiplex MicroRNA Detection.

The development of electrochemiluminescence (ECL) emitters of different colors with high ECL efficiency (ΦECL) is appealing yet challenging for ultrasensitive multiplexed bioassays. Herein, we report the synthesis of highly efficient polymeric carbon nitride (CN) films with fine-tuned ECL emission from blue to green (410, 450, 470, and 525 nm) using the precursor crystallization method. More importantly, naked eye-observable and significantly enhanced ECL emission was achieved, and the cathodic ΦECL values were ca. 112, 394, 353, and 251 times those of the aqueous Ru(bpy)3Cl2/K2S2O8 reference. Mechanism studies showed that the density of surface-trapped electrons, the associated nonradiative decay pathways, and electron-hole recombination kinetics were crucial factors for the high ΦECL of CN. Based on high ΦECL and different colors of ECL emission, the wavelength-resolved multiplexing ECL biosensor was constructed to simultaneously detect miRNA-21 and miRNA-141 with superior low detection limits of 0.13 fM and 25.17 aM, respectively. This work provides a facile method to synthesize wavelength-resolved ECL emitters based on metal-free CN polymers with high ΦECL for multiplexed bioassays.

Rational synthesis of alkaline earth metal vanadates: Structural origin of MgVO3 honeycomb lattice system and its electrochemical analysis for the detection of sulfadiazine

In this study, well-defined alkaline earth metal vanadates, including MgV, CaV, SrV, and BaV, are synthesized using a simple hydrothermal method, and the crystalline structure, morphology, and structural parameters of the synthesized alkaline earth metal vanadates are investigated and compared. Among the alkaline earth metal vanadates, the MgV shows the unique 3D architecture and MgVO3 hexagonal phase with space group R-3c (167) and a single crystalline phase in V4+ valence state and Mg2+ state revealing cation dimerization in 3d1 honeycomb system. Further Raman spectroscopy with Lorentzian peak fitting and X-ray photoelectron spectroscopy exhibit the phase development with a bucky-ball structure. In order to apply the unique feature, the MgV based composite with reduced graphene oxide as a co-catalyst is prepared to examine the practical application for electrochemical sensing of sulfadiazine. The differential pulse voltammetry and the amperometry i-t analysis demonstrate the superior performance of MgV/reduced graphene oxide composite for the sulfadiazine detection including a superior low limit of detection of 9 nM from the differential pulse voltammetry measurements and 3 nM from the amperometry i-t analysis as well as excellent selectivity and long-term stability. These results are attributed to the enhanced electron transfer and ion diffusion from the synergistic effect of unique MgV and reduced graphene oxide. Moreover, the MgV/reduced graphene oxide composite delivers excellent capability in the detection of sulfadiazine in real samples of human blood serum, industrial wastewater, and pharmaceutical tablet.

DNAzyme-driven tripedal DNA walker triggered hybridization chain reaction for label-free electrochemical detection of Alzheimer’s tau protein

The tau protein is considered to be a reliable molecular biomarker of Alzheimer's disease (AD). Developing sensitive and reliable techniques for tau protein detection is a vital task. In this work, we designed a label-free electrochemical aptasensor for tau protein quantification based on Mg2+-DNAzyme (MNAzyme)-driven tripedal DNA walker. With the assistance of MNAzyme, free-running tripedal DNA walkers could rapidly and continually scissor DNA molecular beacon (MBs), and the fragment as a primer initiated the hybridization chain reaction (HCR) process generating a huge amount of long DNA strand containing many adenines. Following that, the strand with long-repeated adenines (HCR product) may absorb numerous AgNPs on the surface of electrode for electrochemical stripping analysis. Benefiting from MNAzyme-tripedal DNA walker and HCR triple signal amplification, we achieved a superior detection limit of 0.43 fM as well as a broad linear range of 1 fM to 0.1 nM. After being applied to tau protein detection in human serum samples, this novel electrochemical aptasensor demonstrated a high degree of anti-interference, and reproducibility, indicating its great potential for bioanalysis in complex biological environments.

CRISPR/Cas12a-based MUSCA-PEC strategy for HSV-1 assay

In the photoelectrochemical sensing, constant potential excitation to get the photoelectrochemical signal is the main excitation signal mode. Novel method for photoelectrochemical signal obtaining is needed. Inspired by this ideal, a photoelectrochemical strategy for Herpes simplex virus (HSV-1) detection with multiple potential step chronoamperometry (MUSCA) pattern was fabricated using CRISPR/Cas12a cleavage coupled with entropy-driven target recycling. In the presence of target, HSV-1, the Cas12a was activated by the H1–H2 complex obtained by entropy-driven, then digesting the circular fragment of csRNA to expose single-stranded crRNA2 and alkaline phosphatase (ALP). The inactive Cas12a was self-assembled with crRNA2 and activated again with the help of assistant dsDNA. After multiple rounds of CRISPR/Cas12a cleavage and magnetic separation, MUSCA, as a signal amplifier, collected the enhanced photocurrent responses generated by catalyzed p-Aminophenol (p-AP). Different from the reported signal enhancement strategies based on photoactive nanomaterials and sensing mechanisms, MUSCA technique endowed the strategy with unique advantages of direct, fast and ultrasensitive. A superior detection limit of 3 aM toward HSV-1 was achieved. This strategy was successfully applied for HSV-1 detection in Human serum samples. The combination of MUSCA technique and CRISPR/Cas12a assay brings broader potential prospect for the detection of nucleic acids.

An aminopeptidase N-based color-convertible fluorescent nano-probe for cancer diagnosis.

Specific cancer diagnosis at an early stage plays a significant role in preventing cancer metastasis and reducing cancer mortality. Thus, exploring specific and sensitive fluorescent probes to realize early cancer diagnosis is an urgent need in clinic. Aminopeptidase N (APN/CD13), overexpressed in numerous malignant tumors, is an important tumor biomarker associated with cancer progression, invasion, and metastasis. In this study, a novel fluorescent molecule APN-SUB, capable of monitoring APN in real time, is encapsulated in a pH-responsive block copolymer (termed APN-SUB nanoprobe) for cancer diagnosis. APN-SUB contains a fluorophore center and a trigger moiety (leucine group), which is covalently conjugated on the fluorophore with an amide bond. The hydrolysis of the amide bond in APN-SUB activated by APN leads to a red shift of maximum fluorescence emission wavelength from 495 nm to 600 nm, realizing dual-color transformation from green to red. Moreover, the APN-SUB nanoprobe with pH-responsiveness is prepared to improve the accumulation and the release rate in the tumor region. It is worth noting that the APN-SUB nanoprobe exhibits good performance for APN imaging, namely, superior limit of detection (0.14 nU mL-1), excellent selectivity and strong photostability. More importantly, the APN-SUB nanoprobe can be successfully employed as a color-convertible fluorescent probe for cancer diagnosis by tracking the activity of APN with high specificity and sensitivity in vivo, demonstrating its potential value for cancer diagnosis.

2-Hydrazinoterephthalic Acid as a Novel Negative-Ion Matrix-Assisted Laser Desorption/Ionization Matrix for Qualitative and Quantitative Matrix-Assisted Laser Desorption/Ionization–Mass Spectrometry Analysis of N-Glycans in Peach Allergy Research

Glycans recently attracted considerable attention as the proposal of cross-reactive carbohydrate determinants for food allergy. Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is powerful in analyzing biomolecules, while its applications in glycans are still challenging. Herein, a novel reactive matrix-assisted laser desorption/ionization (MALDI) matrix, 2-hydrazinoterephthalic acid, was rationally designed and synthesized. It provides uniform co-crystallization with glycans and only produces deprotonated ions with high intensities in the negative-ion mode. In combination with sinapic acid, a rapid and high-throughput method was established for on-target analysis of glycans with a superior limit of detection at the femtomole level and a good linearity (R2 > 0.999). Furthermore, the established method was successfully applied to quantify N-glycans in different cultivars and tissues of peach [Prunus persica (L.) Batsch]. Our work suggests the potential role of N-glycans as biomarkers for food-borne allergy and lays a methodological foundation for the elucidation of the possible relationship between carbohydrate epitopes and food allergy.

Stable enzymatic curve platform and ultrafast catalytic kinetic endows MnSiO3 oxidase mimic with high reliability and supersensitivity

Over the past decades, advanced nanomaterial mediated intrinsic enzymatic colorimetric biosensing has been widely explored in assays and diagnostics. However, low affinity towards substrate and unstable detected curve platform leads to unsatisfactory catalytic kinetic and weak ability to eliminate the interference from difference of individual operation time, significantly decreases their sensitivity and reliability. To our best knowledge, no enzymatic colorimetric detection nanoagents have been reported to have ultrafast catalytic kinetic and stable enzymatic curve platform with satisfactory and reliable accuracy. Herein, a MnSiO3 oxidase mimic was first reported with supersensitivity and high reliability in the paradigm for colorimetric detection of biothiols. The experiment results reveal that the supersensitivity is attributed to its ultrafast affinity towards substrate mediated an excellent catalytic kinetic (Km = 17 μM) and superior limit of detection (10 nM for GSH), which is superior to the previously reported methods. The presence of SiO32− ions further improves the stability of oxidized substrate, provides a stable detected curve platform (∼10 min) and finally exhibits a high reliable accuracy whether addition of test samples at any timepoint within 10 min, which could eliminate the interference of individual operation time. In addition, MnSiO3 is practicable for specific analysis of biological fluids (fetal calf serum and cancer cellula) and design of visual logic gates. Hence, this MnSiO3 oxidase provides a promising solution for biosensing with super-sensitivity and high reliability.

DNAzyme-driven tripedal DNA walker mediated signal-on and label-free for electrochemical detection of α-synuclein oligomers

In the case of Parkinson’s disease (PD), the soluble α-synuclein (α-syn) oligomer is considered to be a reliable molecular biomarker. Developing easy-to-prepare, cheap, sensitive, and reliable techniques for the detection of α-synuclein oligomers is therefore a vital task. In this work, based on Mg2+-dependent DNAzyme (MNAzyme) -driven tripedal DNA walker tactics, we designed an innovative label-free and signal-on electrochemical aptasensor for α-syn oligomer quantification. α-syn oligomer-triggered tripedal DNA walkers outperformed common DNA walkers with the larger area of walking and accelerated walking kinetics, and facilitated greater amplification efficiency. With the assistance of MNAzyme, free-running tripedal DNA walkers could rapidly and continually scissor DNA hairpins (HPs), thereby unlocking numerous active G-quadruplex-forming sequences. Afterwards, G-quadruplex/hemin complexes could be formed by hemin further recognizing these G-quadruplexes and generated an enhanced current signal. Benefiting from tripedal DNA walker and MNAzyme dual signal amplification, we achieved a superior detection limit of 0.46 fM as well as a broad linear range of 1 fM to 10 pM. After being applied to α-syn oligomer detection in human serum samples, this novel electrochemical aptasensor demonstrated a high degree of sensitivity, anti-interference, and reproducibility, indicating its great potential for bioanalysis in complex biological environments.

Fast responding and recovering of NO2 sensors based on Ni-doped In2O3 nanoparticles

In this work, Ni-doped In2O3 nanoparticles were successfully fabricated via a simple metal-organic framework-derived solvothermal method. The synthesized Ni-In2O3 exhibited as ultrafine nanoparticles with an average size of 13 nm. Gas sensing test results demonstrated that the sensor composed of Ni-doped In2O3 (2 mol%) nanoparticles showed fast response/recovery properties, and the response and recovery speeds toward 10 ppm NO2 were 2 and 2 s, respectively. Furthermore, the response value to 10 ppm NO2 was about 70 at the optimum working temperature of 200 °C exhibiting high sensitivity of the sensors. Additionally, the sensor indicated a superior low detection limit of 5 ppb. These characteristics make Ni-doped In2O3 nanoparticles a desiring candidate for rapid detection of NO2. The possible mechanism of enhanced sensing properties was discussed in detail. The Debye-scale nanoparticles furnish abundant adsorption sites. High oxygen vacancies content provides more electrons to accelerate NO2 excitation. Furthermore, the catalytic action of Ni2+ improved the response/recovery speed. The Ni-doped In2O3 nanoparticles are reasonable to be an ideal substitution for fabricating rapid NO2 detection devices in the future.

Sensitivity of Campylobacter jejuni Virulence genes flaA,mapA and hipO by Polymerase chain reaction

Campylobacter jejuni is more frequently associated with zoonotic bacterial cause of foodborne gastroenteritis in humans. Effective diagnosis of C. jejuni infection in various matrix like foods of animal origin, environment and human is crucial to maintain public health. Since molecular diagnosis of C. jejuni carries several advantages over conventional microbial culture techniques, in this study, the limit of detection for the selected virulence genes of C. jejuni (flaA,mapA and hipO) were evaluated to know the suitability of them to be used as molecular diagnostic targets for early detection of C. jejuni by in- house designed primers by conventional PCR. Analytical sensitivity of these genes were assessed in terms of Colony Forming Units (103 CFU/ ml, 102 CFU/ ml, 101 CFU/ ml, 100 CFU/ ml) and DNA concentration (100 ng,10 ng, 1 ng, 100 pg, 10 pg and 1 pg ) of C jejuni cultures. Results revealed that the primers targeting flaA have superior limit of detection as 10CFU and 1pg of C. jejuni DNA. Whereas mapA and hipO have 10 CFU; 10 pg DNA and 100 CFU ;10 ng DNA detection limit respectively. Gene mapA had comparable detection limits in terms of CFU with flaA but found to be less sensitive with respect to DNA concentration but hipO has 102 fold lesser limit of detection.

Electrochemical sensor amplified with cellulose nanofibers/Fe3O4 composite to the monitoring of hydrazine as a pollutant in water and wastewater samples

A quite swift and sensitive analytical instrument was designed in this work to detect and monitor hydrazine in various water and wastewater samples. The glassy carbon electrode (GCE) was amplified using cellulose nanofibers/Fe3O4 composite (CNF–Fe3O4/NC) for monitoring hydrazine in the concentration range of 0.001 - 140 M with a superior detection limit of 0.5 nM. Results showed a diffusion control process for the oxidation of hydrazine at the surface of CNF–Fe3O4/NC/GCE. Under the optimum condition (pH=8.0), the oxidation current of hydrazine was improved by about 2.3 times and the oxidation potential was reduced by about 60 mV at the surface of CNF–Fe3O4/NC/GCE compare to unmodified GCE. A standard addition method was employed to assess CNF–Fe3O4/NC/GCE's capability for the detection of hydrazine in water and wastewater samples, and a recovery range of 97.6 % to 104.9 % was noted.

Sansevieria trifasciata biomass-derived activated carbon by supercritical-CO2 route: Electrochemical detection towards carcinogenic organic pollutant and energy storage application

Activated carbon (AC) has been widely used for electrochemical applications, such as electrochemical sensors, energy storage applications, etc., due to its fine porous structure, volumetric capacitance, and chemical stability. Supercritical-CO2 (SC-CO2) has a fascinating advantage in material science due to its microbubble cavitation, high diffusivity, and high permeability. In the shed of light, we developed a high porous Sansevieria trifasciata biomass-derived AC by SC-CO2 (SC-ST-AC). For comparison purposes, the AC was also prepared in a conventional approach (C-ST-AC). The prepared ACs were characterized through various spectroscopic and microscopic techniques to study their surface morphological character, structural analysis, and phase purity. The electrochemical performance was evaluated by two different applications: electrochemical detection and energy storage application. Based on the results, the SC-ST-AC exhibits higher porous architecture in their morphology and high phase purity with amorphous nature than C-ST-AC. In the preliminary electrochemical analysis, SC-ST-AC achieved higher performance than C-ST-AC. Thus, SC-ST-AC is applied to the real-time application and it exposed a superior limit of detection (0.005 μM L−1) and sensitivity (0.854 μA μM−1 cm−2) towards MA sensing and higher specific capacitance (342.5 F/g for 2 A/g) with 92.09 % of retention at high current density. Thereby, we suggest the SC-CO2 method is a promising approach to develop a highly porous carbon material with excellent electrochemical performance.

Re-engineering of CUP1 promoter and Cup2/Ace1 transactivator to convert Saccharomyces cerevisiae into a whole-cell eukaryotic biosensor capable of detecting 10 nM of bioavailable copper

While copper is an essential micronutrient and a technologically indispensable heavy metal, it is toxic at high concentrations, harming the environment and human health. Currently, copper is monitored with costly and low-throughput analytical techniques that do not evaluate bioavailability, a crucial parameter which can be measured only with living cells. We overcame these limitations by building upon yeast S. cerevisiae's native copper response and constructed a promising next-generation eukaryotic whole-cell copper biosensor. We combined a dual-reporter fluorescent system with an engineered CUP1 promoter and overexpressed Cup2 transactivator, constructing through four iterations a total of 16 variants of the biosensor, with the best one exhibiting a linear range of 10-8 to 10-3 M of bioavailable copper. The engineered variant distinguishes itself through superior specificity, detection limit, and linear range, compared to other currently reported eukaryotic and prokaryotic whole-cell copper biosensors. Moreover, the variant serves as a dual-sensing reporter for Cu2+ detection and cell viability, disregards non-bioavailable copper and other heavy metals, is relatively independent of the cell's physiological status, and was validated on real-world samples which contained interfering substances. Finally, by re-engineering the transactivator, we altered the system's sensitivity and growth rate while assessing the performance of Cup2 with heterologous activation domains. Thus, in addition to presenting the next-generation whole-cell copper biosensor, this work urges for an iterative design of eukaryotic biosensors and paves the way toward higher sensitivity through transactivator engineering.

Silver nanoparticle-coated polydopamine-copper hybrid nanoflowers as ultrasensitive surface-enhanced Raman spectroscopy probes for detecting thiol-containing molecules

In this study, silver nanoparticle-coated polydopamine-copper phosphate hybrid nanoflowers (Ag-PDA-Cu3(PO4)2 NFs) were synthesized and demonstrated to serve as efficient surface-enhanced Raman spectroscopy (SERS) probes for detecting thiol-containing molecules such as benzenethiol and thiocholine. Ag-PDA-Cu3(PO4)2 NFs were fabricated by forming PDA-Cu3(PO4)2 NFs through the nucleation of Cu3(PO4)2 on the PDA surface via interaction between Cu2+ and the free amine groups of dopamine, followed by the anisotropic growth of Cu3(PO4)2 crystals into flower-like microparticles. The NFs were then incubated with silver nitrate for in situ reduction to form Ag nanoparticles (NPs) on the surface of the NFs. The resulting hybrid NFs were demonstrated to act as SERS probes, sensitively detecting thiol-containing molecules, based on the successful interaction between Ag NPs and the thiol group (S-H) of the target molecules. The SERS intensities of benzenethiol and thiocholine at various concentrations were analyzed and found to yield superior limits of detection of 800 and 60 pM, respectively. Therefore, Ag-PDA-Cu3(PO4)2 NFs could be excellent SERS probes for detecting various thiol-containing molecules, particularly to determine the status of patients exposed to thiol-containing pesticides.

Dual mode assay of glutathione with Tb-doped g-C3N4/MnO2 nanoconjugates as fluorescence probe and Mn as elemental target

Glutathione (GSH) plays important roles in various physiological processes, thus highly sensitive assay of GSH and timely warning of its variation at trace level in complex biological matrixes is of great significance. However, this is challenging due to the coexisting reductive biomolecules and dynamic change of GSH levels in responding to various stimuli which remain largely unexploited. Herein, we report a dual mode protocol for the assay of GSH based on nanoconjugate g-C3N4:Tb/MnO2 between MnO2 nanosheets and terbium-doped g-C3N4 (g-C3N4:Tb) nanosheets. MnO2 moiety effectively quenches the emission at 546 nm from Tb3+ in the nanoconjugate, which is restored under the reduction of MnO2 by GSH to ensure fluorescence turn-on assay of GSH. Meanwhile, the generated Mn2+ facilitates inductively coupled plasma mass spectrometry (ICP-MS) detection to endow indirect highly sensitive assay of GSH. Fluorescence mode derived a limit of detection (LOD) of 0.17 μmol L−1 within a linear range of 0.5–160 μmol L−1, while ICP-MS resulted in a superior LOD of 0.016 μmol L−1 within 0.05–160 μmol L−1. Both detection modes provide excellent selectivity to GSH. The dual mode platform was validated by GSH assay in cell lysates. It was further demonstrated by monitoring the variation of dynamic change of GSH level under CuSO4 or cisplatin induced GSH consumption.