Fluorescence Resonance Energy Transfer Mechanism Research Articles

Towards the Development of an Optical Biosensor for the Detection of Human Blood for Forensic Analysis.

Blood is a common biological fluid in forensic investigations, offering significant evidential value. Currently employed presumptive blood tests often lack specificity and are sample destructive, which can compromise downstream analysis. Within this study, the development of an optical biosensor for detecting human red blood cells (RBCs) has been explored to address such limitations. Aptamer-based biosensors, termed aptasensors, offer a promising alternative due to their high specificity and affinity for target analytes. Aptamers are short, single-stranded DNA or RNA sequences that form stable three-dimensional structures, allowing them to bind to specific targets selectively. A nanoflare design has been employed within this work, consisting of a quenching gold nanoparticle (AuNP), DNA aptamer sequences, and complementary fluorophore-labelled flares operating through a fluorescence resonance energy transfer (FRET) mechanism. In the presence of RBCs, the aptamer-flare complex is disrupted, restoring fluorescence and indicating the presence of blood. Two aptamers, N1 and BB1, with a demonstrated binding affinity to RBCs, were selected for inclusion within the nanoflare. This study aimed to optimise three features of the design: aptamer conjugation to AuNPs, aptamer hybridisation to complementary flares, and flare displacement in the presence of RBCs. Fluorescence restoration was achieved with both the N1 and BB1 nanoflares, demonstrating the potential for a functional biosensor to be utilised within the forensic workflow. It is hoped that introducing such an aptasensor could enhance the forensic workflow. This aptasensor could replace current tests with a specific and sensitive reagent that can be used for real-time detection, improving the standard of forensic blood analysis.

Construction of fluorescent aptasensor based on graphene oxide for the detection of metronidazole in food

Aiming at the detection of metronidazole (MNZ) residues in food, a high sensitivity fluorescent aptasensor was designed, which carboxyfluorescein (FAM)-labeled nucleic acid aptamer (FAM-MNZ) as the core probe and graphene oxide (GO) as an efficient fluorescence quencher. The principle is that GO adsorbs the aptamer onto the surface, causing short-range contact between the fluorescent group of the aptamer and GO. Due to its sp2 hybridized domains, GO undergoes fluorescence resonance energy transfer (FRET). Thus, the fluorescence is quenched. When MNZ is added, it preferentially forms a stable complex with the aptamer without FRET. Under optimized conditions, milk samples can be accurately detected with a detection limit of 0.033 μM. In addition, molecular docking, lumo electron orbital simulations, and experimental methods were used to explore the effect of different average radial sizes of single-layer GO on sensing performance. It is shown that GO with a larger average size makes it easy for aptamers to be regularly arranged on its surface. This also provides a basis for electron transfer, resulting in higher fluorescence quenching ability through the FRET mechanism. Therefore, the constructed fluorescent aptamer sensor has a significant application value in food detection.

Visualization of the degradation of long-acting microneedles and correlation of drug release in vivo based on FRET mechanism

This study introduces a live imaging technique for real-time, non-invasive monitoring of drug release from long-acting microneedles using FRET (Fluorescence Resonance Energy Transfer). Employing Cy5.5 and Cy7 as FRET pairs and levonorgestrel as the model drug, we fabricated microneedles with varying PLGA molecular weights, demonstrating distinct release profiles. The FRET-PLGA-10-MN demonstrated a rapid drug release profile, reaching nearly complete release within a two-day period, while FRET-PLGA-30-MN showed a sustained release over four days. Sensitized Emission FRET (SE-FRET) optimized the imaging process, providing a robust correlation between FRET signals and drug absorption. This method surpasses traditional pharmacokinetic studies by offering a more efficient and comprehensive analysis of microneedle release dynamics in vivo, paving the way for enhanced long-acting microneedle design and therapeutic outcomes. Statement of significance1. FRET technology was applied to microneedle drug delivery system for the first time, which realized real-time, quantitative and non-invasive monitoring of drug release process.2. The long-term microneedle technique was combined with sensitized emission method, and the FRET remaining ratio was innovatively used to investigate the FRET characteristics of microneedles, and the fluorescence ratio of FRET and donor double-channel was quantitatively calculated.3. The correlation between visual fluorescence images of FRET effect and semi-quantitative calculation results based on fluorescence intensity and drug release in vivo with drug-loaded microneedles was analyzed.

Preparation of Carbon Quantum Dot with Copper Nanoparticles Using Mugwort Leaves as Carbon Source to Construct FRET Fluorescent Sensor for Melamine Detection

AbstractCarbon quantum dots (CQDs) have gained extensive attention due to their excellent properties and wide applications. In this study, we selected the common Chinese herb mugwort as the carbon source and employed the microwave heating method to synthesize CQDs with a quantum yield of 13.54 %. These CQDs exhibited blue fluorescence under UV light irradiation. Furthermore, we constructed a fluorescence resonance energy transfer (FRET) mechanism by combining CQDs with copper nanoparticles (CuNPs) for the detection of melamine. The detection limit for melamine was determined to be 0.83 nmol/L, with a linear range of 1–100 nmol/L. The results demonstrated the potential of this sensing system for the sensitive and selective detection of melamine.

Enhanced Sensitivity and Accuracy of Tb3+-Functionalized Zirconium-Based Bimetallic MOF for Visual Detection of Malachite Green in Fish.

The ratiometric fluorescent probe UiO-OH@Tb, a zirconium-based MOF functionalized with Tb3+, was synthesized using a hydrothermal method. This probe employs the fluorescence resonance energy transfer (FRET) mechanism between Tb3+ and malachite green (MG) for the double-inverse signal ratiometric fluorescence detection of MG. The probe's color shifts from lime green to blue with an increasing concentration of MG. In contrast, the monometallic MOFs' (UiO-OH) probe shows only blue fluorescence quenching due to the inner filter effect (IFE) after interacting with MG. Additionally, the composite fluorescent probe (UiO-OH@Tb) exhibits superior sensitivity, with a detection limit (LOD) of 0.19 μM, which is significantly lower than that of the monometallic MOFs (25 μM). Moreover, the content of MG can be detected on-site (LOD = 0.94 μM) using the RGB function of smartphones. Hence, the UiO-OH@Tb probe is proven to be an ideal material for MG detection, demonstrating significant practical value in real-world applications.

Liposomal fusion of plant-based extracellular vesicles to enhance skin anti-inflammation

This study reports a hybrid extracellular vesicle (EV)/liposome system developed through vesicular membrane fusion between anti-inflammatory Hydrangea macrophylla leaf EVs (HML-EVs) and terpinen-4-ol/azelamide monoethanolamine-loaded liposomes. Successful liposomal fusion between HML-EVs and terpinen-4-ol/azelamide monoethanolamine-loaded-liposome membranes, confirmed using the two-color fluorescence resonance energy transfer mechanism, enabled the scaled production of a stable hybrid HML-EV/liposome dispersion at a length scale of 100–200 nm. We show that the hybrid EV/liposome significantly inhibits apoptosis by nitric oxide and tumor necrosis factor-α production. Furthermore, HML-EV/liposomes can inhibit the synthesis of protease-activated receptor-2, interleukin-6, c-Jun, and thymic stromal lymphopoietin, thus exhibiting anti-inflammatory performance. These findings highlight that the hybrid EV/liposome system established in this study alleviates skin irritation and improves skin anti-inflammation.

A coumarin-naphthalimide-based ratiometric fluorescent probe for nitroxyl (HNO) based on an ICT-FRET mechanism

Nitroxyl (HNO) is an important reactive nitrogen that is associated with various states in physiology and pathology and plays a unique function in living systems. So, it is important to exploit fluorescent probes with high sensitivity and selectivity for sensing HNO. In this paper, a novel ratiometric fluorescent probe for HNO was developed utilizing intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) mechanisms. The probe selected coumarin as energy donor, naphthalimide as energy receptor and 2-(diphenylphosphino)benzoate as the sensing site for detecting HNO. When HNO was not present, the 2-(diphenylphosphino)benzoate unit of the probe restricted electron transfer and the ICT process could not occur, leading to the inhibition of FRET process as well. Thus, in the absence of HNO the probe displayed the intrinsic blue fluorescence of coumarin. When HNO was added, the HNO reacted with the 2-(diphenylphosphino)benzoate unit of the probe to yield a hydroxyl group which resulting in the opening of ICT process and the occurring of FRET process. Thus, after providing HNO the probe displayed yellow fluorescence. In addition, the probe showed good linearity in the ratio of fluorescence intensity at 545 nm and 472 nm (I545 nm/I472 nm) with a concentration of HNO (0.1–20 μM). The probe processed a detection limit of 0.014 μM and a response time of 4 min. The probe also specifically identified HNO over a wide pH scope (pH = 4.00–10.00), including physiological conditions. Cellular experiments had shown that this fluorescent probe was virtually non-cytotoxic and could be applied for ratiometric sensing of HNO in A549 cells.

Synthesis of P, N-dopped carbon nanosheets for highly sensitive fluorescence analysis of nitrofuran antibiotics in fish

The misuse of antibiotics has caused serious impacts on food safety and human health, making it crucial to develop rapidly and highly sensitive methods for detecting trace nitrofuran antibiotics (NFs). In this study, phosphorus, nitride-doped carbon nanosheets (PN/CNs) were synthesized using a simple hydrothermal method based on graphitic carbon nitride. This prepared material showed excellent water solubility and stable optical properties. A new fluorescence sensing platform based on PN/CNs was constructed for the highly sensitive detection of four NFs. This sensitivity was mainly attributed to the fluorescence resonance energy transfer (FRET) mechanism. The limits of detection for nitrofurazone, nitrofurantoin, furazolidone and furaltadone were determined to be 13.41, 15.24, 16.37 and 19.94 nM, respectively. The high sensitivity and selectivity of PN/CNs for these four NFs were thoroughly evaluated by the Stern-Volmer equation and FRET quenching efficiency. This proposed method exhibited high sensitivity and can be successfully applied to detect NFs in fish.

Construction of nitrogen-doped carbon dots-based fluorescence probe for rapid, efficient and sensitive detection of chlortetracycline

Antibiotics are widely used in clinical medicine due to their excellent antibacterial abilities. As typical emerging pollutants, their misuse can lead to excess antibiotics entering the environment, causing antimicrobial resistance and leading to serious health problems via food chain. Herein, a nano-fluorescent probe based on nitrogen-doped carbon dots (N-CDs) was constructed for the sensitive detection of chlortetracycline (CTC). N-CDs with stable fluorescence were synthesized by hydrothermal method using alizarin red and melamine as raw materials. The N-CDs exhibited significant independence to excitation wavelength. The fluorescence of N-CDs was significantly quenched by CTC ascribing to the fluorescence resonance energy transfer mechanism. The concentration of N-CDs, solution pH and incubation time were optimized to obtain the optimal detection parameters. Under optimal conditions, CTC exhibited excellent linearity over the range of 20–1200 μg/L, and the detection limit was 8.74 μg/L. The method was validated with actual water samples and achieved satisfied spiked recoveries of 97.6–102.6%. Therefore, the proposed method has significant application value in the detection of CTC in waters.

A hydroxyl-rich covalent organic framework for the precisely selective fluorescence sensing of explosives with high sensitivity

Covalent organic Frameworks (COFs) have become a new platform for functional research and material design. A novel covalent organic skeleton (DHB-TFP COF) was synthesized from 2-hydroxybenzene-1,3,5-tricarbaldehyde and 3,3′-dihydroxybenzidine using Schiff base reaction. DHB-TFP COF is a highly stable porous crystalline material and exhibits exceptional thermal and chemical resistance. DHB-TFP COF exhibited a selective and sensitive “turn-off” fluorescence response to 4-NP in ethanol, and TNP not only significantly quenched the fluorescence of DHB-TFP COF but also caused the obvious red-shift. The fluorescence intensity of DHB-TFP COF exhibited a linear correlation with the concentration of 4-NP with a detection limit of 0.40 μM. Furthermore, the maximum fluorescence peak observed for DHB-TFP COF demonstrated a linear relationship with TNP concentration with a detection limit of 11.15 μM. DHB-TFP COF exhibited satisfactory recovery in the detection of 4-NP and TNP in actual water sample indicating its practical application potential. The O atoms of rich hydroxyl and N atoms of C = N present on the surface of DHB-TFP COF scaffold can establish strong hydrogen bonds with 4-NP and TNP, facilitating their mutual interaction. The spectra studies indicated that the fluorescence quenching mechanism can be attributed to the absorption competitive quenching (ACQ) and fluorescence resonance energy transfer (FRET) mechanism. This study not only proposed the approach for synthesizing novel structured organic frameworks, but also developed a highly selective and sensitive fluorescence chemical sensor for identifying and detecting 4-NP and TNP.

Harnessing fluorescence resonance energy transfer for improved solar still performance with zinc oxide nanoparticles and activated carbon

The Single Slope Corrugated Wick type Solar Distillers (SWS) have attracted significant research funding owing to their simple preparation process and excellent durability against heat and moisture. However, there is a recognized need to enhance their solar energy conversion efficiency. The utilization of ZnO nanoparticles (Z) in SWS is limited by their light absorption capacity, resulting in suboptimal thermal energy conversion and solar energy absorption. In this investigation, we propose an innovative method known as Fluorescence Resonance Energy Transfer (FRET), combining crystallized Z with activated carbon (AC) derived from areca nut shells. This novel approach substantially boosts the thermal efficiency of solar energy utilization in SWS by facilitating efficient energy transfer from ZAC to water.The FRET technique enables the effective transfer of energy from ZAC to water and is comprehensively analyzed. By utilizing Z as donors and AC as acceptors, the photoluminescence emitted by ZAC can be absorbed by both components, thereby increasing the carrier population as of Corrugated Wick-type towards the condenser face within SWS. The evaporation rate from water to the condensing surface is significantly higher in SWS with ZAC compared to conventional wick-type solar stills (CWS), attributed to the efficient heat transfer facilitated through multi-dimensional heterojunctions within ZAC. The energy and charge transfer processes are optimized for both summer and winter operating conditions. The ZAC-based SWS exhibits exceptional resilience in various ambient conditions, resulting in a substantial 33.989 % enhancement in distillation efficiency during summer and a notable 31.199 % improvement in winter. The incorporation of ZAC elevates the production of distillate water to 6.325 liters/m2 per day in summer and 5.840 liters/m2 per day in winter (24 h). The energy distribution among particle components is extensively scrutinized using the FRET mechanism.

Fluorescent Molybdenum Disulfide Quantum Dots for Sensitive Detecting Curcumin in Food Samples through FRET Mechanism.

A selective and sensitive fluorometric assay was developed for specific determination of curcumin (Cur) based on fluorescence resonance energy transfer (FRET) between molybdenum disulfide quantum dots (MoS2 QDs) and Cur. The MoS2 QDs were prepared via a one-step hydrothermal protocol using sodium molybdate dihydrate, L-cysteine (Cys) as precursors, and sodium cholate (SC) as a modification agent. The as-prepared MoS2 QDs possessed maximum fluorescence emission at 460nm with a 20% of fluorescence quantum yield (FQY). It was found that the fluorescence of MoS2 QDs could be quantitatively quenched by Cur through FRET mechanism. Therefore, Cur could be detected in the range of 0.1-20µg mL- 1 with a detection limit of 5 ng mL- 1. Additionally, the developed MoS2 QDs based fluorescent assay has been successfully applied for real food sample analysis with satisfactory results.

A fluorescent MOF and its synthesized MOF@cotton composite: Ratiometric sensing of vitamin B2 and antibiotic drug molecule

Here, we demonstrated the synthesis of a zinc based luminescent MOF, 1 (NDC = 2,6- naphthalenedicarboxylate) for the ratiometric detection of biomarker riboflavin (RBF; vitamin B2) in water dispersed medium. Further, this MOF detected two other antibiotic drug molecules, nitrofurantoin (NFT) and nitrofurazone (NZF). The detection of these analytes is very quick (∼seconds), and the limit of detection (LOD) for RBF, NZF and NFT are calculated as 16.58 ppm, 47.63 ppb and 56.96 ppb, respectively. The detection of these analytes was also comprehended by solid, solution, cost-effective paper strip method i.e., triphasic identification capabilities. The sensor is reusable without losing its detection efficacy. The sensor further showed the recognition abilities of these antibiotics in real field samples (river water, urine and tablet) and RBF in vitamin B2 pills and food samples (milk and cold drinks). The sensing merit of 1 urged us to fabricate of 1@cotton fabric composite, which exhibited the colorimetric detection of these analytes. In-depth experimental analysis suggested that the occurrence of photo-induced electron transfer (PET), fluorescence resonance energy transfer (FRET), and the inner filter effect (IFE) are the possible sensing mechanisms for the recognition of the antibiotics drug. The FRET mechanism is responsible for the recognition of RBF. The sensing mechanism is further supported by the theoretical analysis and the excited lifetime measurement.

Establishment of a graphene quantum dot (GQD) based steroid binding assay for the nuclear progesterone receptor (pgr)

Previously, we established a homogeneous assay for membrane progesterone receptor alpha (mPRα) ligands by conjugating semiconductor nanoparticles known as graphene quantum dots (GQDs) to mPRα. When mixed with a progesterone-BSA-fluorescein isothiocyanate conjugate (P4-BSA-FITC), fluorescence occurred by fluorescence resonance energy transfer (FRET) but was reduced by the ligand-receptor binding activity. The established way showed ligand specificity as mPRα protein. In this study, we tried to establish the same way for nuclear progesterone receptor (Pgr). The ligand-binding domain (LBD) of zebrafish Pgr (zPgrLBD) was expressed as a fusion protein with glutathione S-transferase (GST) (GST-zPgrLBD). The recombinant protein was then purified and coupled with GQDs to produce GQD-conjugated GST-zPgrLBD (GQD-GST-zPgrLBD). When mixed with a P4-BSA-FITC and activated by 370 nm light, fluorescence at 520 nm appeared by FRET mechanism. Fluorescence at 520 nm was reduced by adding free progesterone to the reaction mixture. Reduction of fluorescence was induced by zPgr ligands but not by steroids or chemicals that do not interact with zPgr. The results showed the formation of a complex of GQD-GST-zPgrLBD and P4-BSA-FITC with ligand-receptor binding. The binding of the compounds was further confirmed by a radiolabeled steroid binding assay. A homogenous ligand-binding assay for nuclear progesterone receptor has been established.

Fluorescence/electrochemical dual-mode strategy for Golgi protein 73 detection based on molybdenum disulfide/ferrocene/palladium nanoparticles and nitrogen-doped graphene quantum dots.

Golgi protein 73 (GP73) is a new serum marker associated with early diagnosis and postoperative assessment of hepatocellular carcinoma (HCC). Herein, an electrochemical/fluorescence dual-signal biosensor was designed for determination of GP73 based on molybdenum disulfide/ferrocene/palladium nanoparticles (MoS2-Fc-PdNPs) and nitrogen-doped graphene quantum dots (NGQDs). GP73 aptamer (Apt) was labeled with NGQDs to form the NGQDs-Apt fluorescence probe. MoS2-Fc-PdNPs served not onlyas the fluorescence quencher but also as electrochemical enhancer. The sensing platform (NGQDs-Apt/MoS2-Fc-PdNPs) was formed based on the fluorescence resonance energy transfer (FRET) mechanism. In the presence of GP73, the specific binding of NGQDs-Apt to GP73 interrupted FRET, restoring the fluorescence of NGQDs-Apt at λex/em = 348/438nm and enhancing the oxidation current of Fc in MoS2-Fc-PdNPs at 0.04V through differential pulse voltammetry (DPV). Under the optimal conditions, the DPV current change and fluorescence recovery have a good linear relationship with GP73 concentration from 1.00 to 10.0ng/mL. The calibration equation for the fluorescence mode was Y1 = (0.0213 ± 0.00127)X + (0.0641 ± 0.00448) and LOD was 0.812ng/mL (S/N = 3). The calibration equation of the electrochemical mode was Y2 = (3.41 ± 0.111)X + (1.62 ± 0.731), and LOD of 0.0425ng/mL (S/N = 3). The RSDs of fluorescence mode and electrochemical mode after serum detection were 1.62 to 5.21% and 0.180 to 6.62%, respectively. By combining the electrochemical and fluorescence assay, more comprehensive and valuable information for GP73 was provided. Such dual-mode detection platform shows excellent reproducibility, stability, and selectivity and has great application potential.

Damage-indicating and self-healing anticorrosion coatings based on fluorescence resonance energy transfer and photothermal shape memory mechanism

Self-healing coatings, which possess the ability to repair damage and restore corrosion resistance without significant human intervention, have become a hot topic in corrosion protection research. In this paper, (±)-10-camphorsulfonic acid-doped polyaniline is synthesized and then combined with copolyurethane (copPU) to form the photothermal shape memory composite polymer (CSPA-copPU). An aggregation-induced emission agent, named N’,2-bis[(E)-5-chloro-2-hydroxybenzylidene] hydrazine-1-carbohydrazide, is synthesized and applied to create a synergistic fluorescence system with a prepared chelation-enhanced fluorescence (CHEF) agent, named Rhodamine Benzimidazole. Under the CHEF behavior in response to Fe3+ and the fluorescence resonance energy transfer effect, the system exhibits a strong and sensitive fluorescence response to corrosion-generated Fe3+. Using electrospinning technology, CSPA-copPU@Fl fibers are prepared with CSPA-copPU as the shell and a mixture of fluorescent agents as the core solution and applied to create the composite coatings. The coatings effectively indicate damage in the form of fluorescence, providing guidance for infrared laser repair. CSPA facilitates the passivation of exposed steel. Under irradiation by an infrared laser, the surface temperature reaches the glass transition temperature of copPU and the epoxy binder. Through softening expansion and diffusion entanglement of molecular chains, scratches in the coatings are closed and repaired, and the corrosion resistance is restored to a level of intact coatings.

Excellent ratiometric two-photon fluorescent probes for hydrogen sulfide detection based on the fluorescence resonance energy transfer mechanism.

Fluorescence resonance energy transfer (FRET) is an important mechanism to design ratiometric fluorescent probes that are able to detect analytes quantitatively according to the ratio of two well-resolved emission signals. Two-photon (TP) fluorescent probes can realize the detection in living cells and tissues with deeper penetration depth, higher resolution, and lower photodamage in contrast to one-photon fluorescent probes. However, to date, fabricating TP-FRET ratiometric fluorescent probes possessing large two-photon absorption (TPA), high fluorescence quantum yield and perfect FRET efficiency is still challenging. Consequently, to develop excellent TP-FRET ratiometric probes and explore the relationship between their molecular structures and TP fluorescence properties, in this paper, we designed a series of H2S-detecting TP fluorescent probes employing the FRET mechanism based on an experimental probe BCD. Thereafter, we comprehensively evaluated the TP sensing performance of these probes by means of time-dependent density functional theory and quadratic response theory. Furthermore, we determined energy transfer efficiency and fluorescence quantum yield. Significantly, through regulating benzene-fused positions, we successfully improved fluorescence quantum yield and TPA cross-section simultaneously. Large spectral overlap between energy donor emission and acceptor absorption was achieved and near perfect energy transfer efficiency was acquired for all the studied probes. We revealed that these probes exhibit two well-resolved TPA bands, which are contributed by FRET donors and acceptors, respectively. Especially, both the wavelengths and the cross-sections of the two TPA bands agree well with those of energy donors and acceptors, which is the unique TPA spectral profile of FRET probes and has never been previously reported. Moreover, we proposed an excellent TP-FRET probe BCD3 and its product molecule BCD3-H2S, which exhibit large Stokes (141 nm and 88 nm) and emission shifts (5931 cm-1), as well as greatly increased TP action cross-sections (24-fold and 60-fold) in the near-infrared region with respect to BCD and BCD-H2S. Our detailed study can give an insight into the efficient design of novel TP-FRET fluorescent probes.

Enhanced detection of acrylamide using a versatile solid-state upconversion sensor through spectral and visual analysis

Acrylamide (AM) generally forms in high-temperature processes and has been classified as a potential carcinogen. In this study, we put forward a maneuverable solid-state luminescence sensor using polydimethylsiloxane (PDMS) as the matrix coupled with upconversion nanoparticles as the indicator. The core-shell upconversion nanoparticles emitting cyan light were uniformly encapsulated in PDMS. Then it was further modified with complementary DNA of AM aptamer. The nanocrystalline fluorescein isothiocyanate isomer (FITC), coupled with AM aptamer, was attached to the surface of PDMS. FITC effectively quenched the upconversion luminescence through fluorescence resonance energy transfer (FRET). The introduction of AM resulted in preferentially bound to aptamer caused the separation of the quencher and the donor, and led to luminescence recovery. The developed sensor was applied for both spectral and visual monitoring, demonstrating a detection limit (LOD) of 1.00 nM and 1.07 nM, respectively. Importantly, in the actual foodstuffs detection, there is no obvious difference between the results of this study and the standard method, which indicates the developed method has good accuracy. Therefore, this solid-state sensor has the potential for on-site detection using a smartphone device and an Android application.

Applications of Optical Method As an Effective Platform for Progesterone Sensing Using Carbon Dots and Graphene Oxide

Today, ‘Hormonal imbalance’ is a significant concern worldwide that lead to various types of complications in human body. For instance, abnormal levels of steroid hormones, such as progesterone are associated with irregular or absent menstrual periods, reproductive disorders, infertility, cardiovascular diseases, and cancer. Nowadays, progesterone is being excessively consumed as oral contraceptives, menopausal hormone therapy and treating infertility, resulting into the deleterious effects due to its endocrine disrupting activity. Furthermore, its presence as a potent endocrine disruptor in surface or environmental waters and various daily use products is another concern. Therefore, monitoring progesterone hormone is vital in environmental samples because of the adverse effects on reproductive health and causing hormonal imbalance. Herein, we have developed optical photoluminescence (PL) method implementing carbon dots (CDs) and graphene oxide (GO) based fluorescence resonance energy transfer (FRET) mechanism for progesterone hormone sensing. In this method, firstly progesterone-specific antibodies are covalently functionalized to CDs whose fluorescence has been quenched (turn off) by adding GO. However, the presence of progesterone increases the distance between donor and acceptor moieties and turns-on the fluorescence by displacing GO off the surface of CDs which in turn substantially reduces the FRET efficiency. Various optimization steps have been performed under control experiments to tune the fluorescence of CDs and the concentration of graphene oxide for maximum efficiency. In conclusion, a linear relationship is achieved in between PL intensity and different progesterone concentrations (10-900 nM) with 13.8 nM detection limits (R2=0.974). The structural and morphological analysis (XPS, and FT-IR) revealed the structural and surface functionalities of CDs. Finally, the potential of the developed biosensor has been explored in water matrices.

A fluorescent sensor based on Zn(II)-coodination polymers bearing mixed ligands for the sensitive detection of riboflavine, imidacloprid and nitenpyram

Two new 2D Zn(II) coordination polymers (BAO28 and BAO29), formulated as [Zn(DIN)(HPT)]DMF·2H2O (BAO28) and [Zn(DIN)(HPT)]·2H2O (BAO29) (H2HPT = 5‑hydroxy-isophthalic acid, DIN = 1,4-di(imidazol-1-yl)naphthalene and DMF = N,N-dimethylformamide), were successfully synthesized under solvothermal conditions. Fluorescence analysis showed that BAO28 proceeded with a DIN ligand-based emissive fluorescence. More importantly, the recoverable multi-responsive fluorescent sensor BAO28 was used for fluorescent detection of imidacloprid (IMI), nitenpyram (NTP), and riboflavine (VB2) in a neutral buffer solution with high sensitivity and a low detection limit. Moreover, the sensing of the pesticides by BAO28 was mainly due to the competitive absorption of excitation and emission light by the sensor with that of the pesticides. Furthermore, for the sensing of riboflavine, in addition to the internal filtration effect (IFE) and fluorescence resonance energy transfer (FRET) mechanisms, the sensing mechanism was simultaneously attributed to photoinduced electron transfer.