An ultra-sensitive "turn-off" fluorescent sensor for the trace detection of rifampicin based on glutathione-stabilized copper nanoclusters

Rapid and reliable ratiometric fluorescence detection of nitro explosive 2,4,6-trinitrophenol based on a near infrared (NIR) luminescent Zn(II)-Nd(III) nanoring

Rapid and quantitative detection of 2,4,6-trinitrophenol (TNP) is very crucial for homeland security, military application, and environment protection. Herein, a nine-metal Zn(II)-Nd(III) nanoring 1 with a diameter of 2.3 nm was constructed by the use of a long-chain Schiff base ligand, which shows ratiometric fluorescence response to TNP with high selectivity and sensitivity. The fluorescence sensing behavior of 1 to TNP is expressed by a first-order equation I1060nm/I560nm = -0.0128*[TNP] + 0.9723, which can be used to quantitatively analyze TNP concentrations in solution. The limits of detection (LODs) to TNP based on the ligand-centered (LC) and Nd(III) emissions of 1 are 5.93 μM and 3.18 μM, respectively. The fluorescence response mechanism to TNP is attributed to the competitive absorption effect and photoinduced electron transfer (PET). The luminescence quenching of 1 is dominated by static process.

Rapid and reliable ratiometric fluorescence detection of isoquercitrin based on a high-nuclearity Zn(II)-Nd(III) nanomolecular sensor

Rapid and quantitative detection of isoquercitrin (Isq) has been attracting much attention due to its outstanding pharmacological and physiological activities. Herein, an interesting 48-metal Zn(II)-Nd(III) nanocluster (1, molecular sizes 1.3 × 2.8 × 3.1 nm) with salen-type Schiff base ligand was constructed as molecular sensor for the luminescence detection of Isq. 1 exhibits visible ligand-centered emission and NIR luminescence of Nd(III), and shows ratiometric fluorescence response to Isq with high sensitivity even in the presence of other interferences. The fluorescence sensing behavior can be expressed by a second-order equation I1060nm/I480nm = A*[Isq]2 + B*[Isq] + C, which is used to quantitatively analyze the Isq concentrations in DMF and FCS. The LODs to Isq for the ligand-centered and lanthanide emissions of 1 in DMF are 0.21 μM and 0.11 nM, respectively. The quenching of the ligand-centered emission of 1 caused by Isq is attributed to the competitive absorption of light energy and "inner effect", while, the luminescence enhancement is due to the "antenna effect".

A novel fluorescent sensor for selective rifampicin detection based on the bio-inspired molecularly imprinted polymer-AgInS2/ZnS quantum dots

A fluorescent sensing material based on the ternary core-shell quantum dots with outstanding optical properties and a bio-inspired molecularly imprinted polymer (MIP) as a recognition element has been prepared for selective detection of rifampicin (RFP). Firstly, AgInS2/ZnS core/shell quantum dots (ZAIS QDs) were prepared by a hydrothermal process. Then, the fluorescent sensor was prepared by coating these QDs by a dopamine-based MIP layer. The fluorescence of MIP@ZAIS QDs was quenched by RFP probably due to the photoinduced electron transfer process. The quenching constant was much higher for MIP@ZAIS QDs than the non-imprinted polymer@QDs, indicating that MIP@ZAIS QDs could selectively recognize RFP. Under the optimized conditions, the sensor had a good linear relationship at the RFP concentration range of 5.0 to 300 nM and the limit of detection was 1.25 nM. The respond time of the MIP@ZAIS QDs was 5 min, and the imprinting factor was 6.3. It also showed good recoveries ranging from 98 to 101%, for analysis of human plasma samples. The method is simple and effective for the detection of RFP and offers a practical application for the rapid analysis of human plasma samples.

Highly sensitive sensing of DPA by lanthanide metal-organic frameworks and detection of fiber membranes

The detection of 2,6-pyridinecarboxylic acid (DPA), as a biomarker of Bacillus anthracis, has attracted wide attention. In previous reports of DPA detection, fluorescent probes may not have high specificity. Therefore, the rational design and development of fluorescent sensors with excellent performance is of great significance for the detection of DPA. In this study, two novel lanthanide metal-organic frameworks (Ln-MOFs) were synthesized by hydrothermal method using 3-polyfluorobiphenyl-3 ', 4,5 ' -tricarboxylic acid (H2FPTA) as ligand. Studies have shown that Ln-MOFs can detect DPA in real time, with detection limits of 0.54 μM and 0.67 μM, respectively, and have a high recovery rate (95 % -108 %) in fetal bovine serum. As a self-calibration sensor, other substances in the blood can be clearly distinguished by a two-dimensional fluorescence code diagram. After the Ln-MOFs were spun into nanofiber membranes, they responded quickly to DPA. This increases practicability and provides a promising idea for the development of simple and efficient ratio sensors.

Functional Group-Assisted Fluorescence Sensing Platform for Nanomolar-Level Detection of an Antineoplastic Drug and a Neurotransmitter from Environmental Water and Human Biofluids

A fast, sensitive, selective, and biocompatible dual sensor of an antineoplastic medication (methotrexate) and a neurotransmitter (adrenaline) is still being searched by present-day scientists. To overcome this issue, we have designed a functionalized, robust, bio-friendly luminescent MOF for the sensitive, selective, and rapid monitoring of methotrexate and adrenaline. This probe is the first ever reported MOF-based fluorescence sensor of methotrexate and second only for adrenaline. This fluorescence probe has a very low limit of detection (LOD) of 0.34 and 11.2 nM for adrenaline and methotrexate, respectively. The sensor can detect both the targeted analytes rapidly within 5 s. It can also detect adrenaline and methotrexate from human blood serum and urine accurately and precisely. This reusable sensor is equally efficient in detecting methotrexate from environmental water specimens. Biocompatible, user-friendly, and inexpensive chitosan@MOF@cotton composites were fabricated for the detection of adrenaline and methotrexate from the nanomolar to the micromolar range by the naked eye under a fluorescence lamp. This probe displayed high reproducibility, precision, and accuracy in sensing methotrexate and adrenaline. Fluorescence resonance energy transfer (FRET) and the inner filter effect (IFE) are the possible mechanisms for adrenaline and methotrexate sensing, respectively. The possible mechanism was supported by using required instrumental techniques and theoretical simulations.

State of the Art on Developments of (Bio)Sensors and Analytical Methods for Rifamycin Antibiotics Determination

This review summarizes the literature data reported from 2000 up to the present on the development of various electrochemical (voltammetric, amperometric, potentiometric and photoelectrochemical), optical (UV-Vis and IR) and luminescence (chemiluminescence and fluorescence) methods and the corresponding sensors for rifamycin antibiotics analysis. The discussion is focused mainly on the foremost compound of this class of macrocyclic drugs, namely rifampicin (RIF), which is a first-line antituberculosis agent derived from rifampicin SV (RSV). RIF and RSV also have excellent therapeutic action in the treatment of other bacterial infectious diseases. Due to the side-effects (e.g., prevalence of drug-resistant bacteria, hepatotoxicity) of long-term RIF intake, drug monitoring in patients is of real importance in establishing the optimum RIF dose, and therefore, reliable, rapid and simple methods of analysis are required. Based on the studies published on this topic in the last two decades, the sensing principles, some examples of sensors preparation procedures, as well as the performance characteristics (linear range, limits of detection and quantification) of analytical methods for RIF determination, are compared and correlated, critically emphasizing their benefits and limitations. Examples of spectrometric and electrochemical investigations of RIF interaction with biologically important molecules are also presented.

Three-dimensional porous reduced graphene oxide modified electrode for highly sensitive detection of trace rifampicin in milk

Antibiotic overuse poses a serious food safety problem. Therefore, it is of great importance to develop efficient assays that respond to antibiotics to establish early-warning mechanisms. Here, we prepared a three-dimensional (3D) porous reduced graphene oxide (pRGO) modified electrode, which was characterized by scanning electron microscopy and transmission electron microscopy. As a result of the introduction of the 3D pRGO film, the electrocatalytic activity was considerably improved, which could efficiently trigger the redox reaction of rifampicin (RIF). By employing differential pulse voltammetry, the reduction peak current of RIF showed a good linear relationship with the logarithm of the RIF concentration in the range 1.0 × 10^-9 to 1.0 × 10^-7 mol L^-1. The linear equation was i_p (-10^-6 A) = 3.11 + 0.28 log c_RIF (R² = 0.9908) with a detection limit of 2.7 × 10^-10 mol L^-1 (S/N = 3). Additionally, the final electrode displayed long stability, good reproducibility and high selectivity, and could detect trace RIF in milk with satisfactory results. This study reveals the great potential in utilizing 3D pRGO to develop efficient electrochemical sensors for safeguarding food safety.

A copper nanoclusters probe for dual detection of microalbumin and creatinine

A fluorescent probe based on glutathione-capped copper nanoclusters (GSH-CuNCs) was developed for the detection of dual targets, human serum albumin (HSA) and creatinine, in human urine. The GSH-CuNCs were synthesized by a one-pot green method using ascorbic acid as a reducing agent. The detection of HSA was in a turn-on mode via electrostatic interaction in a basic condition while the detection of creatinine was in a turn-off mode via non-covalent bonding in an acidic condition. Under optimal conditions, the linear range and detection limit of HSA were 5.0 nM to 150 nM and 1.510 ± 0.041 nM, while those of creatinine were 30 μM to 1000 μM and 13.0 ± 1.0 μM. This easily fabricated nanocluster probe provided a fast response with high sensitivity, and good selectivity. Recoveries from urine samples were in the range of 81.44 ± 0.25 to 109.22 ± 0.57% for HSA and 80.57 ± 0.16 to 109.0 ± 0.10% for creatinine. The urinary analytical results from the fluorescent probe were in good agreement (P > 0.05) to those obtained from immunoturbidimetric and enzymatic methods, signifying the excellent performance of this sensing system.

Regulatable Detection of Antibiotics Based on a Near-IR-Luminescent Tubelike Zn(II)-Yb(III) Nanocluster

A tubelike Zn(II)-Yb(III) cluster, [Zn6Yb5L5(HL)(NO3)4(DMF)6(EtOH)4(H2O)4] (1; DMF = N,N-dimethylformamide and EtOH = ethanol; molecular size 1.5 × 1.8 × 2.9 nm), was synthesized from a new long-chain Schiff base ligand. 1 exhibits a regulatable near-IR-luminescent response to nitrofuran antibiotics (NFAs) and fluoroquinolones with high sensitivity, which is not influenced by other antibiotics. The quenching constants of NFAs and fluoroquinolones range from 0.55 × 104 to 8.8 × 104 M-1, and the detection limits of 1 to them are from 4.2 × 10-4 to 2.6 × 10-5 M. It also shows a luminescent response to real antibiotic drugs containing NFAs and fluoroquinolones.

Construction of a Cd8Tb4 nanoring for luminescence response to 2,6-dipicolinic acid as an anthrax biomarker

One 12-metal Cd(ii)–Tb(iii) nanoring (1.2 × 2.8 × 2.8 nm) was constructed from a flexible Schiff base ligand, and it shows luminescent response to 2,6-dipicolinic acid with high sensitivity and selectivity.

A dual-channel colorimetric and fluorescent sensor for the rapid and ultrasensitive detection of kanamycin based on gold nanoparticles-copper nanoclusters

In this work, a dual-channel assay was constructed for the colorimetric and fluorescent detection of kanamycin (KAN) based on gold nanoparticles (Au NPs) and copper nanoclusters (Cu NCs). Initially, the fluorescence of Cu NCs was quenched by 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT)-functionalized Au NPs due to the inner filter effect (IFE). The existence of KAN acted as a molecular bridge to interact with AHMT via hydrogen bonds and induced the aggregation of AHMT-Au NPs, leading to a change in the color of the gold colloidal solution from reddish-violet to blue within 2 min. Moreover, the aggregated AHMT-Au NPs can weaken its IFE toward Cu NCs and result in fluorescence restoration. With the sensor employed here, the concentration of KAN can be quantitatively analyzed through double channels, and a low LOD (limit of detection) of 1.9 nM and 1.2 nM was realized by the colorimetric and fluorescent method, respectively. Benefitting from the short response time, high sensitivity, and good reliability, the established assay offered great opportunities for the on-site monitoring of antibiotics in environmental samples.

Ratiometric fluorescence determination of chlortetracycline based on the aggregation of copper nanoclusters triggered by aluminum ion

The aggregation-induced emission (AIE) characteristic of copper nanoclusters (CuNC) was for the first time used to construct a ratiometric fluorescence probe (CuNC-Al³⁺) for detection of chlortetracycline (CTC). Aluminum ion (Al³⁺) can aggregate free CuNC and make it emit a bright and stable red fluorescence. A slight excess of Al³⁺ in CuNC-Al³⁺ solution can form a CTC-Al³⁺ complex to limit the conformational rotation of CTC molecule and enhance CTC fluorescence. So, the red fluorescence of CuNC-Al³⁺ probe and the enhanced CTC fluorescence are used as a reference signal and a response signal to detect CTC, respectively. The method developed shows a good linear relationship between the CTC concentration and the fluorescence intensity ratio (I₄₉₅/I₅₇₅) in the range 0.1-3.0 µM, and the detection limit is 25.3 nM (S/N = 3). In addition, the fluorescent color of CuNC-Al³⁺ probe changes from red to yellow-green as the concentration of CTC increases. Based on this observation, a fluorescent test paper has also been fabricated. Schematic illustration of Al³⁺ inducing CuNC to produce AIE performance and detecting CTC.

Ratiometric fluorescent detection of dipicolinic acid as an anthrax biomarker based on a high-nuclearity Yb18 nanoring

An 18-metal lanthanide nanoring [Yb₁₈(L¹)₈(HL²)₂(OAc)₂₀(MeOH)₈(EtOH)₆(H₂O)₄] (1), which shows a ratiometric fluorescent response to DPA, was constructed through the strategy of using two types of polydentate organic ligands. The addition of DPA increases the visible ligand-centered emission, but decreases the NIR lanthanide luminescence of 1. The limit of luminescent detection of 1 for DPA is 1.5 μM. The high fluorescence sensitivity of 1 to DPA is not affected by the existence of interferents such as aromatic carboxylates and ions.

A hydrostable samarium(III)-MOF sensor for the sensitive and selective detection of tryptophan based on a "dual antenna effect"

Tryptophan (Trp) is one of the essential amino acids, which plays important roles in biological systems and the normal growth of human beings, and it is of great significance to be able to detect Trp in a rapid, efficient, and sensitive way. Herein, a 3D network metal-organic framework ([Sm₂(BTEC)_1.5(H₂O)₈]·6H₂O) with excellent thermal and water stability was synthesized by a hydrothermal method. Interestingly, it could discriminate Trp from other natural amino acids in aqueous solution through a significant fluorescence enhancement effect, and showed high detection sensitivity (LOD = 330 nM) and outstanding anti-interference ability. The sensor system was successfully applied to the detection of Trp in practical samples, so it was expected to be a sensitive and efficient Trp sensor. In addition, the sensing mechanism was explained in detail by a series of characterization methods combined with density functional theory (DFT). There were many coordination water molecules in the crystal structure of the complex. Based on the small steric hindrance and molecular structure of water molecules, it provided the possibility for coordination interaction between Trp and Sm³⁺. On the other hand, the triplet energy level (T1) of Trp matched with the ⁴G_5/2 vibrational energy level of Sm³⁺, so Trp could be used as the second "antenna molecule" besides 1,2,4,5-benzenetetracarboxylic acid (H₄BTEC). Therefore, it effectively broadened the way for Sm-MOF to absorb excitation light.

Smartphone-assisted visual ratio-fluorescence detection of hypochlorite based on copper nanoclusters

A sensitive naked eye and ratio-fluorescence sensor for Curcumin (CCM) and hypochlorite (ClO^-) determination based on copper nanoclusters (Cu NCs) was developed. The fluorescence of the Cu NCs can be quenched due to inner filter effect (IFE) between CCM and Cu NCs, and the ratio fluorescence probe was formed. After adding ClO^- to Cu NCs-CCM system, the phenolic and methoxy groups of CCM were oxidized to quinones, then the fluorescence of CCM was quenched and the fluorescence of Cu NC was restored. Moreover, the continuous detection of CCM and ClO^- is accompanied by the change of solution color. Therefore, CCM and ClO^- semiquantitative visual and fluorescence dual channel detection were realized. The detection results show that the detection based on Cu NCs-CCM probe has a wide detection range (0-412 µM) and low detection limit (24 µM), and a good recovery rate is obtained in adulterated milk and tap water detection. Furthermore, smartphone was introduced for image digital colorimetric analysis through the acquisition, recognition and RGB data processing of solution colors, providing an effective scheme for the field rapid detection of hypochlorite.

Optical biosensors - Illuminating the path to personalized drug dosing

Optical biosensors are low-cost, sensitive and portable devices that are poised to revolutionize the medical industry. Healthcare monitoring has already been transformed by such devices, with notable recent applications including heart rate monitoring in smartwatches and COVID-19 lateral flow diagnostic test kits. The commercial success and impact of existing optical sensors has galvanized research in expanding its application in numerous disciplines. Drug detection and monitoring seeks to benefit from the fast-approaching wave of optical biosensors, with diverse applications ranging from illicit drug testing, clinical trials, monitoring in advanced drug delivery systems and personalized drug dosing. The latter has the potential to significantly improve patients' lives by minimizing toxicity and maximizing efficacy. To achieve this, the patient's serum drug levels must be frequently measured. Yet, the current method of obtaining such information, namely therapeutic drug monitoring (TDM), is not routinely practiced as it is invasive, expensive, time-consuming and skilled labor-intensive. Certainly, optical sensors possess the capabilities to challenge this convention. This review explores the current state of optical biosensors in personalized dosing with special emphasis on TDM, and provides an appraisal on recent strategies. The strengths and challenges of optical biosensors are critically evaluated, before concluding with perspectives on the future direction of these sensors.

Highly Luminescent Copper Nanoclusters Stabilized by Ascorbic Acid for the Quantitative Detection of 4-Aminoazobenzene

As one of the widely studied metal nanoclusters, the preparation of copper nanoclusters (Cu NCs) by a facile method with high fluorescence performance has been the interest of researchers. In this paper, a simple, green, clean, and time-saving chemical etching method was used to synthesize water-soluble Cu NCs using ascorbic acid (AA) as the reducing agent. The as-prepared Cu NCs showed strong green fluorescence (with a quantum yield as high as 33.6%) and high ion stability, and good antioxidant activity as well. The resultant Cu NCs were used for the detection of 4-aminoazobenzene (one of 24 kinds of prohibited textile compounds) in water with a minimum detection limit of 1.44 μM, which has good potential for fabric safety monitoring.

Multiwalled Carbon Nanotubes-CeO2 Nanorods: A "Nanonetwork" Modified Electrode for Detecting Trace Rifampicin

Herein, a "nanonetwork" modified electrode was fabricated based on multiwalled carbon nanotubes and CeO₂ nanorods. Scanning electron microscopy, X-ray powder diffraction and zeta potential were employed to characterize this electrode. Multiwalled carbon nanotubes negatively charged and CeO₂ nanorods positively charged form "nanonetwork" via electrostatic interaction. The performance of the CeO₂ nanorods-based electrode remarkably improved due to the introduction of multiwalled carbon nanotubes. The detection of rifampicin (RIF) was used as a model system to probe this novel electrode. The results showed a significant electrocatalytic activity for the redox reaction of RIF. Differential pulse voltammetry was used to detect rifampicin, the reduction peak current of rifampicin linear with the logarithm of their concentrations in the range of 1.0 × 10^-13-1.0 × 10^-6 mol/L, The linear equation is i_p = 6.72 + 0. 46lgc, the detect limit is 3.4 × 10^-14 mol/L (S/N = 3). Additionally, the modified electrode exhibits enduring stability, excellent reproducibility, and high selectivity. This strategy can be successfully used to detect trace rifampicin in samples with satisfactory results.