Internal Probe Research Articles

Construction of a ratiometric electrochemical sensor for Bisphenol A detection by coupling nonionic surfactant-decorated conductive carbon black with ferricyanide probe

In this work, a novel ratiometric electrochemical sensor for bisphenol A (BPA) detection was facilely constructed by coupling conductive carbon black (VXC-72R) with ferricyanide probe. The VXC-72R was decorated with nonionic surfactant Tween to enhance the sensitivity and coated on glassy carbon electrode (GCE), whereas K3[Fe(CN)6] was introduced into electrolyte solution as an internal reference probe to realize dual-signal outputs. The present ratiometric electrochemical sensor achieved a highly sensitive and selective detection of BPA in PBS solution (pH = 7.0), with a linear range of 0.08–40.0 μM and detection limit of 0.05 μM. Moreover, it has been successfully applied to the determination of BPA in real lake water and milk samples with the satisfactory recoveries rates of 94.8–102.3 %.

A magnetic SERS-imprinted sensor for the determination of cardiac troponin I based on proteolytic peptide technology

Acute myocardial infarction is a sudden and high-mortality disease that can be accurately diagnosed by measuring the level of cardiac troponin I in the blood. Currently, cTnI commonly used clinical detection methods usually have excellent sensitivity and are suitable for large-scale sample detection analysis. However, most of these methods are operated through multiple steps of fixation, incubation, reaction and separation, and most of them require professionals to operate complex instruments, which greatly limits their applicability in real-time rapid detection. Therefore, a method that requires low professional skills and can perform rapid detection is necessary. We presents an alternative strategy to quantify cTnI in clinical serum samples using a combination of SERS and magnetic molecularly imprinted polymers (MMIP). MMIPs was synthesized under Polyvinyl Pyrrolidone (PVP) conditions without vinyl modification using characteristic peptide as template, MAA and DMAm as functional monomers. The internal Raman probe 4-MBA was connected through Ag-SH bonds in MMIPs to solve the problem that the target object had no Raman characteristic peak. MMIPs with high magnetic and adsorptive properties showed characteristic absorption peaks at the Raman shift of 1582 cm−1 after specific capture of the target templates. The Raman signals of the 4-MBA were reduced due to shielding effects and the detection range of this method was 0.001–100 ng mL−1. The recoveries and relative standard deviations (RSDs) of the spiked experiments were 103.1%–106.3 % and 3.54 %–7.38 %, respectively. In summary, this work had appropriate sensitivity and specificity, and there was no significant difference in detection results after ELISA verification. It provided a flexible and practical analysis method for detecting cTnI based on SERS technology. In addition, the imprinting materials of other disease markers can be prepared by changing the template molecules, which provides a new idea for the detection of other biomarkers.

Ratiometric electrochemical and impedimetric dual-mode aptasensor based on thionine-functionalized Ti3C2Tx MXene/Pt and Au nanoparticle composites for reliable detection of aflatoxin B1

Rapid and reliable detection of aflatoxin B1 (AFB1) is critical in public health, food safety and environmental control. Herein, a ratiometric electrochemical (EC) and electrochemical impedance spectroscopy (EIS) dual-mode aptasensing platform based on thionine-functionalized Ti3C2Tx MXene/Pt and Au nanoparticle composites (MXene@Thi/PtAuNPs) was constructed for accurate and reliable detection of AFB1. The MXene@Thi/PtAuNPs composites were prepared by a facile and mild approach. The electroactive molecule Thi embedded in MXene could not only inhibit the aggregation of MXene nanosheets, but also act as an internal reference probe to form a ratiometric sensing strategy. The decoration of Pt and Au nanoparticles can further effectively enhance the conductivity and catalytic activity of the composites. The MXene@Thi/PtAuNPs composites were then served as a support to sequentially assemble hairpin DNA (hDNA) and ferrocene-labelled AFB1 aptamer (Fc-Apt) to construct the dual-mode sensor. The developed dual-mode sensor with both ratiometric EC detection (based on IThi/IFc) and EIS detection (based on Ret) can mutually verify the detection results obtained by two modes, offering more accurate and reliable results, which enabled sensitive and reliable AFB1 detection in the concentration range of 10.0 pg mL−1-30.0 ng mL−1 (ratiometric EC mode) and 3.0 pg mL−1-30.0 ng mL−1 (EIS mode), respectively. The sensing platform also demonstrated favorable selectivity, reproducibility and stability, and satisfactory applicability in corn sample, showing great potential in the sensing of mycotoxins in agricultural products.

Ratiometric Electrochemical Detection of Interleukin-6 Using Electropolymerized Methylene Blue and a Multi-Walled Carbon-Nanotube-Modified Screen-Printed Carbon Electrode.

Herein, we report a ratio-based electrochemical biosensor for the detection of interleukin-6 (IL-6). We electropolymerized methylene blue (MB) on the surface of screen-printed carbon electrodes; introduced an internal reference signal probe; modified the carboxylate multi-walled carbon nanotubes on the electrode surface to increase the electrochemically active area; and finally linked the amino-modified IL-6 aptamer to the electrode surface through the Schiff base reaction, with bovine serum albumin (BSA) added to mask non-specific adsorption. After adding IL-6 to the samples, the signal of IMB remained almost unchanged, while the signal of I[Fe(CN)6]3-/4- decreased with increasing IL-6 concentration. Thus, a novel ratiometric electrochemical sensor with a linear range of 0.001~1000.0 ng/mL and a low detection limit of 0.54 pg/mL was successfully developed. The sensor had high repeatability, stability, sensitivity, and practicability. It provides a new method for constructing proportional electrochemical sensors and detecting IL-6.

A General Method for Calibration of Active Scanning Thermal Probes

Scanning thermal microscopy (SThM) is a scanning probe technique aimed at quantitative characterization of local thermal properties at the length scale down to tens of nanometers. With many probe designs and approaches to interpretation of probe responses, there is a need for a universal framework, which would allow probe calibration and comparison of probe performance. Herein, a calibration framework based on an abstracted, formal, probe model for active SThM probes is developed. The calibration can be accomplished through measurements with two or three calibration samples. Requirements for calibration samples are described with examples of structures of suitable samples identified in published literature. A link to a published experimental work indirectly verifying the proposed procedure is provided. The calibration does not require knowledge of internal probe properties and yields a small and universal set of parameters that can be used to quantify thermal resistance presented to the probe by samples as well as to characterize active‐mode SThM probes of any type and at any measurement frequency. How the probe calibration parameters can be used to guide probe design is illustrated. When the calibration approach can be used directly to measure the thermal conductivity of unknown samples is also analyzed.

Combined Threshold Implementation

Physical security is an important aspect of devices for which an adversary can manipulate the physical execution environment. Recently, more and more attention has been directed towards a security model that combines the capabilities of passive and active physical attacks, i.e., an adversary that performs fault-injection and side-channel analysis at the same time. Implementing countermeasures against such a powerful adversary is not only costly but also requires the skillful combination of masking and redundancy to counteract all reciprocal effects.In this work, we propose a new methodology to generate combined-secure circuits. We show how to transform Threshold Implementation (TI)-like constructions to resist any adversary with the capability to tamper with internal gates and probe internal wires. For the resulting protection scheme, we can prove the combined security in a well-established theoretical security model.Since the transformation preserves the advantages of TI-like structures, the resulting circuits prove to be more efficient in the number of required bits of randomness (up to 100%), the latency in clock cycles (up to 40%), and even the area for pipelined designs (up to 40%) than the state of the art for an adversary restricted to manipulating a single gate and probing a single wire.

Simultaneous detection of eight dairy-derived components using multiplex PCR combined with gene membrane chip

Food adulteration poses a significant risk to food safety, especially in the case of milk and dairy products, which have garnered substantial attention from regulatory authorities. In this study, we developed a method for simultaneous detection of eight animal-derived components in milk and dairy products, employing multiplex PCR combined with gene membrane chip. These components encompass cow, yak, buffalo, goat, sheep, horse, donkey, and camel. Eight dairy-derived animal-specific probes, along with eukaryotic internal reference and plant-derived internal reference probes, were designed and immobilized on nylon membranes for hybridization with PCR products, enabling source identification. Utilizing reverse dot blot hybridization, the gene membrane chip facilitates the determination of eight dairy-derived components and the presence of plant-derived components. The method demonstrated an absolute sensitivity of 0.01 ng in the multiplex PCR and membrane chip hybridization system, with a detection limit of 0.1%, meeting market supervision requirements. Upon analysis of 75 commercially available dairy products, a mislabeling rate of 29.33% was revealed. Comparative analysis with conventional PCR and real-time quantitative PCR demonstrated the method's high specificity, good repeatability, and significantly improved detection throughput, thereby enhancing the screening efficiency for adulterants in dairy products and the targeted detection capability.

A preliminary investigation of precise visualization, localization, and resection of pelvic lymph nodes in bladder cancer by using indocyanine green fluorescence-guided approach through intracutaneous dye injection into the lower limbs and perineum.

This study aimed to investigate the feasibility and effectiveness of using indocyanine green (ICG) injected intracutaneously through the lower limbs and perineum for visualized tracking, localization, and qualitative assessment of pelvic lymph nodes (LNs) in bladder cancer to achieve their accurate resection. First, ICG was injected into the LN metastasis model mice lower limbs, and real-time and dynamic in vivo and ex vivo imaging was conducted by using a near-infrared fluorescence imaging system. Additionally, 26 patients with bladder cancer were enrolled and divided into intracutaneous group and transurethral group. A near-infrared fluorescence imaging device with internal and external imaging probes was used to perform real-time tracking, localization, and resection of the pelvic LNs. The mice normal LNs and the metastatic LNs exhibited fluorescence. The metastatic LNs showed a significantly higher signal-to-background ratio than the normal LNs (3.9 ± 0.2 vs. 2.0 ± 0.1, p < 0.05). In the intracutaneous group, the accuracy rate of fluorescent-labeled LNs was 97.6%, with an average of 11.3 ± 2.4 LNs resected per patient. Six positive LNs were detected in three patients (18.8%). In the transurethral group, the accuracy rate of fluorescent-labeled LNs was 84.4%, with an average of 8.6 ± 2.3 LNs resected per patient. Two positive LNs were detected in one patient (12.5%). Following the intracutaneous injection of ICG into the lower limbs and perineum, the dye accumulates in pelvic LNs through lymphatic reflux. By using near-infrared fluorescence laparoscopic fusion imaging, physicians can perform real-time tracking, localization, and precise resection of pelvic LNs.

Development, confirmation, and application of a seeded Escherichia coli process control organism to validate Salmonella enterica serovar Typhi environmental surveillance methods.

Salmonella enterica serovar Typhi (S. Typhi) is the causative agent of Typhoid fever. Blood culture is the gold standard for clinical diagnosis, but this is often difficult to employ in resource limited settings. Environmental surveillance of waste-impacted waters is a promising supplement to clinical surveillance, however validating methods is challenging in regions where S. Typhi concentrations are low. To evaluate existing S. Typhi environmental surveillance methods, a novel process control organism (PCO) was created as a biosafe surrogate. Using a previous described qPCR assay, a modified PCR amplicon for the staG gene was cloned into E. coli. We developed a target region that was recognized by the Typhoid primers in addition to a non-coding internal probe sequence. A multiplex qPCR reaction was developed that differentiates between the typhoid and control targets, with no cross-reactivity or inhibition of the two probes. The PCO was shown to mimic S. Typhi in lab-based experiments with concentration methods using primary wastewater: filter cartridge, recirculating Moore swabs, membrane filtration, and differential centrifugation. Across all methods, the PCO seeded at 10 CFU/mL and 100 CFU/mL was detected in 100% of replicates. The PCO is detected at similar quantification cycle (Cq) values across all methods at 10 CFU/mL (Average = 32.4, STDEV = 1.62). The PCO was also seeded into wastewater at collection sites in Vellore (India) and Blantyre (Malawi) where S. Typhi is endemic. All methods tested in both countries were positive for the seeded PCO. The PCO is an effective way to validate performance of environmental surveillance methods targeting S. Typhi in surface water.

Reagent-Free Lactate Detection Using Prussian Blue and Electropolymerized-Molecularly Imprinted Polymers-Based Electrochemical Biosensors.

Sweat lactate, a promising biomarker for assessing physical performance and health conditions, calls for noninvasive, convenient, and affordable detection methods. This study leverages molecularly imprinted polymers (MIPs) as a synthetic biorecognition element for lactate detection due to their affordability and high stability. Traditional MIPs-based electrochemical sensors often require external redox probes such as ferricyanide/ferrocyanide in the solution to signal the binding between analytes and MIPs, which restricts their applicability. To address this, our study introduces an innovative approach utilizing a layer of Prussian blue (PB) nanoparticles as the internal redox probe on screen-printed carbon electrodes (SPCE), followed by a layer of electropolymerized MIP (eMIP) for molecular recognition, enabling reagent-free lactate detection. The real-time growth of eMIP and the processes of template elution and lactate rebinding were examined and validated using electrochemical surface plasmon resonance (EC-SPR) spectroscopy. The sensor's performance was thoroughly investigated using Differential Pulsed Voltammetry (DPV) and Electrochemical Impedance Spectroscopy (EIS) with samples spiked in 0.1 M KCl solution and artificial sweat. The developed sensors demonstrated a fast and selective response to lactate, detecting concentrations from 1 to 35 mM with a Limit of Detection (LOD) of 0.20 mM, defined by a signal-to-noise ratio of 3 in the DPV measurements. They also exhibited excellent reproducibility, reusability, and a shelf life of up to 10 months under ambient conditions. These eMIP/PB/SPCE-based lactate sensors show considerable potential as point-of-care (POC) devices for sweat lactate detection, and the technology could be adapted for reagent-free detection of a broad spectrum of molecules.

Passive high explosive neutron inspection (PHENIX): a new method to confirm the presence or absence of high explosives for nuclear treaty verification

Advanced instruments and methods need to be developed now to create a technical basis to support the negotiation of future nuclear arms control treaties. One new capability that is anticipated is the ability to confirm either the declared presence or declared absence of high explosive (HE) material in the presence of special nuclear material (SNM). Towards this goal, Passive HE Neutron Inspection (PHENIX) has been developed and demonstrated as a method for confirming the presence or absence of HE in the presence of plutonium. The method exploits the inherent presence of neutrons associated with the decay of plutonium as an internal probe source for performing prompt gamma-ray neutron activation analysis (PGNAA), searching for the presence of HE as revealed by the emission of characteristic gamma rays following neutron absorption in hydrogen and nitrogen which are building blocks of present-day, military-grade HE. Tests using stoichiometrically-correct hemishells of mock HE with plutonium show that a system can be expected to positively confirm the presence or absence of these signatures, supporting determination of HE presence or absence with Pu, in a few hours. To protect other potentially sensitive gamma-ray signatures from a treaty accountable item, an analog information barrier has been conceptualized and tested which physically prevents the collection of gamma-ray spectral data outside of user selected energy windows strategically chosen to view only narrow spectral regions corresponding to the hydrogen (2223.2 keV) and nitrogen (9807.2 keV, 10,318.2 keV, and 10,829.2 keV) PGNAA signatures.

Ratiometric Electrochemical Sensor Using Chitosan@Rhodamine B/Gold Nanoparticles (AuNPs) for the Sensitive Determination of Rutin by Differential Pulse Voltammetry (DPV)

Internal reference probes can effectively eliminate internal and external interferences. Hence, finding a suitable internal reference probe is the key to ratiometric electrochemistry. In this study, a simple and sensitive ratiometric electrochemical sensor for the determination of rutin was prepared for the first time using rhodamine B (Rh B) as an internal reference probe. The modified electrochemical sensor was constructed by electrodepositing gold nanoparticles (AuNPs) on a glassy carbon electrode followed by drop-coating chitosan-immobilized rhodamine B (CS@Rh B). Rh B has a dual function in that it has a stable electrochemical signal (1.18 V) (vs. Ag/AgCl) that is completely separated from the oxidation peak of rutin (0.52 V) to serve as an internal reference probe. At the same time, it synergistically enhances the electrochemical signal of rutin with AuNPs. When differential pulse voltammetry was used for the determination of rutin, the current ratio of I Rutin/I Rh B was employed as the signal for rutin determination with a wide linear range (0.1 to 70 μM) and a low detection line (0.028 μM). The recoveries for the determination of rutin in Coreopsis tinctoria and Buckwheat tea were 95.4%–106% and 95.3%–104%, respectively. This work successfully demonstrated the feasibility of Rh B as an internal reference probe.

A dual-functional Cu-BTC/COOH-MWCNTs ratiometric electrochemical sensing device for the detection of sunset yellow and tartrazine

A ratiometric electrochemical sensor for sunset yellow (SY) and tartrazine (TZ) was constructed by modifying a glassy carbon electrode with a composite of carboxylated multiwalled carbon nanotubes (COOH-MWCNTs) and a redox-active metal–organic frameworks (Cu-BTC MOFs). Cu-BTC served as an internal reference probe with a constant oxidation peak current. The sensor exhibited excellent linearity in the concentration range of 2–200 μM under optimized conditions. The detection limits for SY and TZ were found to be 0.73 μM and 0.78 μM, respectively. When the sensor was used to determine SY and TZ in two carbonated beverages, the resules were good and did not significantly differ from those obtained by UV–Vis spectrophotometry.

Research on Internal Shape Anomaly Inspection Technology for Pipeline Girth Welds Based on Alternating Excitation Detection.

Abnormal formation of girth weld is a major threat to the safe operation of pipelines, which may lead to serious accidents. Therefore, regular inspection and maintenance of girth weld are essential for accident prevention and energy security. This paper presents a novel method for inspecting abnormal girth weld formation in oil and gas pipelines using alternating excitation detection technology. The method is based on the analysis of the microscopic magnetic variations in the welded area under alternating magnetic fields. An internal inspection probe and electronic system for detecting abnormal girth weld formation were designed and developed. The system's capability to identify misalignment, undercutting, root concavity, and abnormal formation height of girth weld was tested by numerical simulation and experimental study. The results show that the detection system can effectively identify a minimum misalignment of 0.5 mm at a lift-off height of 15 mm. The proposed method offers several advantages, such as rapid response, low cost, non-contact operation, and high sensitivity to surface flaws in ferromagnetic pipelines.

Nanoarchitectonics of on–off ratiometric signal amplified electrochemical sensor for chlorpromazine with molecularly imprinted polymer based on Ni-MOF/Fe-MOF-5 hybrid Au nanoparticles

A novel and stable on–off ratiometric electrochemical sensing platform for chlorpromazine (CPZ) detection by combing the selective recognition of molecularly imprinted polymer (MIP) technology and ratiometric quantification strategy. Gold nanoparticles (AuNPs) were first electrodeposited on a bare glassy carbon electrode surface and then modified with a mixture of Ni-MOF/Fe-MOF-5 by drop-coating, and subsequently electropolymerization polythionine (pTHi) as an internal reference to achieve a ratiometric on–off response. The reference signal of pTHi was obtained by the boiling water-bath-assisted in-situ electropolymerization method for the first time. Ni-MOF/Fe-MOF-5 hybrid AuNPs (Ni-MOF/Fe-MOF-5/AuNPs) not only benefited the output signal amplification, but also provided the enlarged surface for immobilization of pThi and MIPs, and served as catalytic active centers to oxidation CPZ. Then, the MIPs membrane was fabricated through in-situ electropolymerization by using CPZ as the template molecule, nicotinamide as a functional monomer. Ratiometric identifying and quantitative sensing model has been proposed based on the combination of MIP membrane as molecular recognition receptor and pTHi used as an internal reference probe, which improves the sensitivity and selectivity of the sensor. Under the optimal conditions, the ratiometric signals of peak current (ICPZ/IpTHi) were linear to CPZ concentration in the range of 0.001–40 μM and 40–900 μM, with the ultralow detection limit of 0.025 μM (S/N = 3). Furthermore, this sensor exhibited high anti-interference ability, reproducibility, satisfactory stability, and outstanding measurement performance in biological samples with favorable recoveries in the range of 98.11–100.81%. Together, the constructed on–off ratiometric MIP sensing platform is a promising tool for the rapid and accurate determination of antipsychotic drugs with high selectivity and stability.

Eddy Current False Indications in Austenitic Steel and Titanium Alloys Heat Exchanger Tubes Activated by Stress

Eddy current non-destructive examination with the internal bobbin type probes is a mandatory test for heat exchanger tube manufacturing due to its high sensitivity to the different type discontinuities. In this paper, we want to highlight the problems related to the false indications in the nonmagnetic austenitic steel and titanium alloys due to magnetic inclusions. There are known origins for magnetic inclusions in stainless steel like chips or filings as a result of ferrous tool application, alloy depletion concerned with oxidation or corrosion, and magnetite deposits. The little-known origin of magnetic inclusions is concerned with stress induced martensitic transformation is shortly analyzed in this report as a possible mechanism for the creation of the magnetic inclusion in austenitic steel as in titanium alloy tubes. The phase transformation and as the result the presence of magnetic inclusions is generated by the activation of the spin magnetic moments of the free electrons under stress influence. These inclusions can radically influence the eddy current signal due to quite large difference in relative magnetic permeability but can be differentiated from real defects by re-inspection of the suspicious tubes at reduced operational frequency. During the eddy current examinations of stainless steel and titanium tubes by an internal probe, the false indications in tubes have been detected. The presence of these isolated indications is located always in the same length of the tested tube. The indications were detected in each tube and the signal amplitude was estimated in the range of 40-50% of the acceptance reference level. In stainless steels, the false indications generated are higher than in titanium alloys.

A ratiometric fluorescent probe based on PIM-1 semiconducting polymer dots for turn-off-on sensing and bioimaging

Herein, we report a simple green platform based on a novel type of polymer dots (Pdots) as a sensitive and rapid “off-on” fluorescent probe for ratiometric Fe3+ and Cu2+ detection. The ratiometric probe has been designed using green-emitting PIM-1 Pdots and red-emitting PFTBT Pdots as detecting probes and internal stable standard probes, respectively. The dual-emission characteristics of PIM-1/PFTBT Pdots allowed us to apply ratiometric ion determination based on aggregation-caused quenching (ACQ) of PIM-1 Pdots at 490 nm, while the red emission intensity kept highly stable. The role of porosity and surface carboxylic groups of PIM-1 to achieve high sensitivity and selectivity using quantum-mechanical calculation and cellular imaging was successfully demonstrated so that the detection limit of 7.4 nM for Fe3+ and 14.8 nM for Cu2+ was obtained. The “on” process with excellent selectivity was realized by the introducing of glutathione (GSH) into PIM-1/PFTBT/Cu2+ and Cytochrome c (Cyt c) into PIM-1/PFTBT/Fe3+ with fluorescence recoveries of the blank sample 92 % and 91 %, respectively. The proposed strategy detects GSH and Cyt c with a good linearity ranging from 300 nM to 1800 nM and 10 nM to 120 nM by the limit of detection of 85.3 nM and 0.6 nM, respectively. This combinational off-on strategy provides a promising nanosensing platform for monitoring Fe3+ and Cu2+ in the environmental samples and introduces a sensitive probe with high biocompatibility for intracellular target imaging.

Detection of Panax notoginseng and its products using a duplex quantitative polymerase chain reaction assay

Panax notoginseng is a traditional Chinese medicinal herb. With its wide applications in medicine, food products, health care, cosmetics and other industries, identification and detection of P. notoginseng have become critical. In this study, we developed a real-time polymerase chain reaction (qPCR) assay with specific and internal control probes based on chloroplast psbA-trnH gene and 18S rDNA to identify and detect P. notoginseng in different products. A specific primer and probe set was designed by comparing psbA-trnH sequence among P. notoginseng, Panax ginseng, Panax quinquefolius and Panax japonicus. Besides, the 18S rDNA gene was used as an internal control. The qPCR condition was optimized with the sensitivity to be 0.005 ng/μL and high specificity. There was no cross-reaction among 18 closely related common Chinese herbs. Detection results of 28 commercially available P. notoginseng products were consistent with the standardized sequencing results. This study provides a rapid, specific and sensitive assay for detection of P. notoginseng in different products.

Au Nanoparticle/CoFc/Metal–Organic Framework as Enzyme-Free Dual-Signal Ratiometric Electrochemical Sensor for In-Situ Determination of Cell-Secreted H2O2

In-situ determination of cell-secreted biomolecules is important for elucidating its regulation of signal transduction pathways, but detecting these low-level endogenous biomolecules is difficult. Herein, using H2O2 as the detection object, we developed an ultrasensitive enzyme-free ratiometric electrochemical sensing platform in a simple and low-cost method for in-situ determination of cell-secreted H2O2, in which ferrocene (Fc) acts as an internal reference probe and nanoflower Au-Co-MOF acts a detection probe. First, flower-like CoFc-MOF was synthesized in situ on flexible carbon cloth (CC) by a one-step hydrothermal method, and then Au-CoFc-MOF/CC was obtained by electrodeposition of gold nanoparticles. The electrochemical measurement results show that the presence of H2O2 increases the reduction peak signal of Co-MOF (−0.32 V), while that of Fc (+0.4 V) is almost unchanged. By taking full advantage of the obviously separated reduction potential of Fc and Co-MOF, the well-designed sensing platform can reflect the concentration of H2O2 based on the IH2O2 – Iblank/IFc value in the 0.5 μM–10 mM range, with a detection limit as low as 32 nM, which is ∼15.6 times lower than the value obtained from the single signal method. In addition, the sensing platform also demonstrates excellent selectivity, reproducibility, stability, and biocompatibility. More significantly, this ratiometric electrochemical sensing platform based on flexible substrate shows great application potential in the in-situ determination of cell-secreted H2O2, which provides a feasible strategy for detecting other active substances released from living cells in clinical diagnosis.

Dual-functional lanthanide-MOF probe nanocomposite based on hydroxyapatite nanowires as fluorescent sensor for ascorbic acid.

Adual-functional lanthanide-MOF nanocomposite probewas designed and constructed for the detection of ascorbic acid (AA). The magnetically functionalized hydroxyapatite nanowires are selected as the carriers and simultaneously loaded with ciprofloxacin (CIP) and terbium metal organic framework to form the internal reference fluorescence probe nanocomposite (Fe3O4-HAPNWs-Tb/MOF-CIP). This dual-functional lanthanide-MOF probe not only combines the respectively unique fluorescence properties of lanthanide MOFs and CIP, but also takes full advantage of the rapid separation properties of the magnetic component. Structural and spectroscopic characterization results have demonstrated the successful synthesis of probe material and the fluorescence mechanism. At a suitable excitation wavelength (295nm), the probe can simultaneously emit characteristic fluorescence of CIP (445nm) and Tb3+ (543nm). In the presence of AA, the ratio of I543/I445 decreases rapidly with increasing of AA concentration. The linear range of determinationis 0.3-40μM with a detection limit of 20.4nM. Thecontents of AA in vitamin C tablets and four fruit juice samples were detected by the composite probe. The spiked recoveries ranged from 82.6 to 104.2% with relative standard deviations (RSD) less than 2.1%, revealing the practical application value of the developed sensor in healthcare and food fields. A novel internal reference fluorescence sensor (Fe O -HAPNWs-Tb/MOF-CIP) was constructed for detecting ascorbic acid by solvothermal and self-assembly techniques, showing excellent selectivity and sensitivity based on the different responses of Tb/MOF and CIP to the target.