A novel fluorescent nanosensor for detection of heparin and heparinase based on CuInS2 quantum dots

Nanosensor based approaches for quantitative detection of heparin

Heparin, being a widely employed anticoagulant in numerus clinical complications, requires strict quantification and qualitative screening to ensure the safety of patients from potential threat of thrombocytopenia. However, the intricacy of heparin's chemical structures and low abundance hinders the precise monitoring of its level and quality in clinical settings. Conventional laboratory assays have limitations in sensitivity and specificity, necessitating the development of innovative approaches. In this context, nanosensors emerged as a promising solution due to enhanced sensitivity, selectivity, and ability to detect heparin even at low concentrations. This review delves into a range of sensing approaches including colorimetric, fluorometric, surface-enhanced Raman spectroscopy, and electrochemical techniques using different types of nanomaterials, thus providing insights of its principles, capabilities, and limitations. Moreover, integration of smart-phone with nanosensors for point of care diagnostics has also been explored. Additionally, recent advances in nanopore technologies, artificial intelligence (AI) and machine learning (ML) have been discussed offering specificity against contaminants present in heparin to ensure its quality. By consolidating current knowledge and highlighting the potential of nanosensors, this review aims to contribute to the advancement of efficient, reliable, and economical heparin detection methods providing improved patient care.

Recent Applications of Quantum Dots in Pharmaceutical Analysis

Nanotechnology has emerged as one of the most potential areas for pharmaceutical analysis. The need for nanomaterials in pharmaceutical analysis is comprehended in terms of economic challenges, health and safety concerns. Quantum dots (QDs)or colloidal semiconductor nanocrystals are new groups of fluorescent nanoparticles that bind nanotechnology to drug analysis. Because of their special physicochemical characteristics and small size, QDs are thought to be promising candidates for the electrical and luminescent probes development. They were originally developed as luminescent biological labels, but are now discovering new analytical chemistry applications, where their photo-luminescent properties are used in pharmaceutical, clinical analysis, food quality control and environmental monitoring. In this review, we discuss QDs regarding properties and advantages, advances in methods of synthesis and their recent applications in drug analysis in the recent last years.

Temperature- and Size-Dependent Photoluminescence of CuInS2 Quantum Dots

We present the results of a temperature-dependent photoluminescence (PL) spectroscopy study on CuInS2 quantum dots (QDs). In order to elucidate the influence of QD size on PL temperature dependence, size-selective precipitation was used to obtain several nanoparticle fractions. Additionally, the nanoparticles' morphology and chemical composition were studied using transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The obtained QDs showed luminescence in the visible-near infrared range. The PL energy, linewidth, and intensity were studied within an 11-300 K interval. For all fractions, a temperature decrease led to a shift in the emission maximum to higher energies and pronounced growth of the PL intensity down to 75-100 K. It was found that for large particle fractions, the PL intensity started to decrease, with temperature decreasing below 75 K, while the PL intensity of small nanoparticles remained stable.

A turn-on fluorescence sensor for detection of heparinase with heparin templated aggregation of tetracationic porphyrin derivative

Heparinase is the only mammalian endoglycosidase that breaks down the commonly used blood-anticoagulant heparin into therapeutically relevant low-molecular-weight-heparin. Importantly, heparinase has been considered a malignant disease diagnostic marker. Thus, it is essential to develop detection scheme for heparinase. However, optical methods for heparinase determination are limited. In the present work, we report a turn-on fluorescence sensor for detection of heparinase that utilizes heparin-templated aggregation of a tetra-cationic porphyrin derivative, TMPyP4+, as a sensing framework. Heparinase cleaves the glycosidic linkage between hexosamine and uronic acid in the structure of heparin to destroy its polyelectrolytic nature that originally causes the aggregation of TMPyP4+. Thus, heparinase leads to dissociation of TMPyP4+ aggregates and generates an optical signal. This system leads to a sensitive and selective response towards heparinase with a Limit of Detection (LOD) of 0.3 pmol/L. Further, the same system is demonstrated to sense a trace amount of Oversulfated Chondrootin Sulphate (OSCS) in heparin, which is a heparin adulterant, by utilizing the fact that OSCS serves as an inhibitor for heparinase activity, which leads to reverse modulation in the photo-physical features of the monomer/aggregate equilibrium of the TMPyP4+-heparin-heparinase system. The sensing mechanism has been thoroughly demonstrated by ground-state absorption, steady-state emission, and time-resolved emission measurements. The selectivity of the sensor was tested using lysozyme, α-amylase, pepsin, trypsin, lipase, and glucose oxidase in the heparinase selectivity study and the method is also validated using another method reported in the literature. The study provides a new approach for the development of optical methods for the detection of heparinase and oversulfated chondroitin sulfate, which is currently limited.

Nanozyme catalysis-assisted ratiometric multicolor sensing of heparin based on target-specific electrostatic-induced aggregation

Monitoring the level of heparin in clinical matrices is significant because of its pivotal role in preventing thrombosis. Compared to traditional single-signal sensors, multi-signal ratiometric detection can provide anti-interference results especially in complicated environments. However, fabricating an easy-to-operation, low-cost and robust sensor for the ratiometric detection of heparin still remains challenging. Here we propose a novel nanosensor for the ratiometric multicolor sensing of heparin with high performance. The sensor is based on the specific electrostatic interaction between the target and a positively charged species generated from nanozyme catalysis. FeMoO₄ nanorods are explored as an oxidase mimic for the first time, showing a high activity at neutral pH to catalyze the colorless 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to blue TMBox with an absorbance at 652 nm. Heparin can induce the rapid aggregation of the produced TMBox intermediate with rich positive charges due to their strong electrostatic interaction, leading to the formation of a purple Heparin-TMBox complex providing a signal at 565 nm. With the increase of heparin, the color changes from blue to indigo and further purple, enabling the multicolor sensing of the target. As a result, ultrasensitive determination of heparin was obtained with a very low detection limit. The fabricated nanosensor could differentiate heparin from complex species with no interferences, and it provided reliable analytical results for heparin in both serum and plasma. With robust performance, low cost and facile fabrication, the sensor holds great potential in monitoring heparin for clinical applications.

Enhanced Photoacoustic Detection of Heparin in Whole Blood via Melanin Nanocapsules Carrying Molecular Agents

Photoacoustic (PA) imaging has proved versatile for many biomedical applications from drug delivery tracking to disease diagnostics and postoperative surveillance. It recently emerged as a tool for accurate and real-time heparin monitoring to avoid bleeding complications associated with anticoagulant therapy. However, molecular-dye-based application is limited by high concentration requirements, photostability, and a strong background hemoglobin signal. We developed polydopamine nanocapsules (PNCs) via supramolecular templates and loaded them with molecular dyes for enhanced PA-mediated heparin detection. Depending on surface charge, the dye-loaded PNCs undergo disassembly or aggregation upon heparin recognition: both experiments and simulation have revealed that the increased PA signal mainly results from dye-loaded PNC-heparin aggregation. Importantly, Nile blue (NB)-loaded PNCs generated a 10-fold higher PA signal than free NB dye, and such PNC enabled the direct detection of heparin in a clinically relevant therapeutic window (0-4 U/mL) in whole human blood (R² = 0.91). Furthermore, the PA signal of PNC@NB obtained from 17 patients linearly correlated with ACT values (R² = 0.73) and cumulative heparin (R² = 0.83). This PNC-based strategy for functional nanocapsules offers a versatile engineering platform for robust biomedical contrast agents and nanocarriers.

Ternary Quantum Dots in Chemical Analysis. Synthesis and Detection Mechanisms

Ternary quantum dots (QDs) are novel nanomaterials that can be used in chemical analysis due their unique physicochemical and spectroscopic properties. These properties are size-dependent and can be adjusted in the synthetic protocol modifying the reaction medium, time, source of heat, and the ligand used for stabilization. In the last decade, several spectroscopic methods have been developed for the analysis of organic and inorganic analytes in biological, drug, environmental, and food samples, in which different sensing schemes have been applied using ternary quantum dots. This review addresses the different synthetic approaches of ternary quantum dots, the sensing mechanisms involved in the analyte detection, and the predominant areas in which these nanomaterials are used.

Employing CuInS2 quantum dots modified with vancomycin for detecting Staphylococcus aureus and iron(iii)

This paper describes a near-infrared quantum dot (CuInS₂ QD)/antibiotic (vancomycin) nanoparticle-based assay for the Staphylococcus aureus and iron(iii) detection. CuInS₂ QDs with good biological tissue permeability and biocompatibility are combined with vancomycin through covalent interaction to form a detection system for two harmful factors. The detection principle of Staphylococcus aureus is mainly the fluorescence quenching caused by the accumulation of CuInS₂@Van QDs on the surface of Staphylococcus aureus. The detection principles of the iron(iii) ion are mainly ascribed to the aggregation of quantum dots and the transfer of charges, which cause the fluorescence signal to change. The linear range of S. aureus and the Fe³⁺ ion is 10³ to 10⁸ CFU mL^-1 and 10-90 μM, respectively. Their detection limits are 665 CFU mL^-1 and 3.5 μM, respectively. The procedure was validated by the quantitation of Staphylococcus aureus and iron(iii) in spiked samples, and was found to demonstrate the feasibility of this method.

Lead halide perovskites with aggregation-induced emission feature coupled with gold nanoparticles for fluorescence detection of heparin

Herein, a new kind of lead halide perovskite (LHP, (C₁₂H₂₅NH₃)₂PbI₄) with aggregation-induced emission (AIE) feature is developed as a fluorescent probe for heparin (Hep). The LHPs exhibit high emission when they aggregate in water. Interestingly, a few picomoles of dispersed gold nanoparticles (AuNPs) can quench the emission of LHPs, but the aggregated AuNPs are invalid. When protamine (Pro) is mixed with AuNPs at first, the negatively charged AuNPs aggregate through electrostatic interaction, producing the AIE recovery. Nevertheless, Hep disturbs the interaction between AuNPs and Pro due to its strong electrostatic interaction with Pro. Therefore, the dispersed AuNPs quench the fluorescence of LHPs again. A response linear range of Hep of 0.8-4.2 ng ml^-1is obtained, and the detection limit is 0.29 ng ml^-1. Compared with other probes for determination of Hep with AuNPs, this strategy exhibits better sensitivity due to the small quantity of AuNPs used. Finally, it is also successfully applied to detect Hep in human serum samples with satisfactory recoveries.

A colorimetric and fluorometric based dual readout approach for effective heparin sensing

Devising fluorescence-based turn-on probes for the specific and sensitive detection of Heparin is of utmost clinical importance. In this contribution, we have identified a molecular rotor based asymmetric cyanine probe, thiazole orange (TO), which enables an efficient colorimetric and fluorimetric detection of Heparin. TO undergoes the formation of emissive H-aggregates upon interaction with Heparin that display an impressive emission enhancement of ~22 fold together with drastic changes in the absorption spectra that yields a prominent colour change in the solution from orange to yellow. These seldom reported emissive H-aggregates of TO, serve as an efficient platform for Heparin detection with a LOD of 19 nM, fluorometrically and 34 nM, colorimetrically. The TO-Heparin complex is also accompanied by a large change in the excited-state lifetime. The TO-Heparin complex has been further utilized for the detection of Protamine, which is the only medically affirmed antitoxin of Heparin. Overall, our sensing system offers several advantages, such as, simple, dual read-out, economic and specific detection of Heparin with longer excitation and emission wavelength, rapid naked eye detection and utilizes an in-expensive commercially available fluoprophore, TO. Most importantly, our sensing system also displays a good performance in the biologically complex human serum matrix.

Recent research on the luminous mechanism, synthetic strategies, and applications of CuInS2 quantum dots

We discuss the synthesis and luminescence mechanisms of CuInS₂ QDs, the strategies to improve their luminous performance and their potential application in light-emitting devices, solar energy conversion, and the biomedical field.

The Photoluminescence and Biocompatibility of CuInS2-Based Ternary Quantum Dots and Their Biological Applications

Semiconductor quantum dots (QDs) have become a unique class of materials with great potential for applications in biomedical and optoelectronic devices. However, conventional QDs contains toxic heavy metals such as Pb, Cd and Hg. Hence, it is imperative to find an alternative material with similar optical properties and low cytotoxicity. Among these materials, CuInS2 (CIS) QDs have attracted a lot of interest due to their direct band gap in the infrared region, large optical absorption coefficient and low toxic composition. These factors make them a good material for biomedical application. This review starts with the origin and photophysical characteristics of CIS QDs. This is followed by various synthetic strategies, including synthesis in organic and aqueous solvents, and the tuning of their optical properties. Lastly, their significance in various biological applications is presented with their prospects in clinical applications.

Heparin sensing based on multisite-binding induced highly ordered perylene nanoaggregates

Heparin sensing based on highly ordered perylene nanoaggregates with ultra-low fluorescence and the use of host–guest complexes to improve the sensitivity.

Lost in (Clinical) Translation: Recent Advances in Heparin Neutralization and Monitoring

The heparin family, which includes unfractionated heparin, low-molecular heparin, and fondaparinux, is a class of drugs clinically used as intravenous blood thinners. To date, issues related to both the reversal of anticoagulation and the blood level determination of the anticoagulant at the point-of-care remain: while the only U.S. Food and Drug Administration (FDA) approved antidote for heparin displays serious efficacy and safety drawbacks, the current assays for heparin monitoring are indirect measurements subject to their own limitations and variations. Herein, we provide an update on the numerous recent chemical approaches to tackle these issues, from which it is clear that some new antidotes and sensors for heparin certainly have the potential to exceed current clinical standards. This review aims to review a field that requires close collaborations between physicians, biologists, and chemists in order to foster advances toward clinical translation.

Fabrication of Orange-Emitting Organic Nanoparticle-Protamine Conjugate: Fluorimetric Sensor of Heparin

Among the diverse sensing techniques, fluorimetric detection dominates over the other methods because of its rapid signaling, high selectivity and sensitivity, and operational simplicity. This present article delineates fabrication of a fluorescent organic nanoparticle-protamine (FONP-Pro) conjugate for selective and sensitive detection of heparin simply by exploitation of the aggregation-induced emission (AIE) property of the FONPs. Naphthalene diimide-based bola-type amphiphilic molecules (NDI-1) comprise a naphthyl residue and a 3-aminopyridyl unit at both terminals, forming organic nanoparticles in a dimethyl sulfoxide-water binary solvent mixture, and exhibited AIE through excimer formation. The presence of naphthyl residue in the molecular backbone facilitates the intramolecular charge transfer to generate orange-emitting (λ_em = 594 nm) AIE-luminogen (AIE-gen). The aminopyridine residues within NDI-1 induced negative surface charge on NDI-1 FONPs, which facilitated interaction with positively charged protamine (Pro) to construct FONP-Pro conjugates. Formation of this NDI-1 FONP-Pro conjugate through the interaction between Pro and FONP drastically reduced the orange emission intensity (fluorescence off) of the AIE-gens. Interestingly, addition of heparin to this FONP-Pro conjugate turned on the fluorescence signal of FONPs through unwinding of the Pro from the FONP surface because of a strong binding affinity between heparin and Pro. Formation of the FONP-Pro conjugate and fluorimetric sensing of heparin was investigated by monitoring the change in emission behavior of NDI-1 FONPs. Also, the heparin-sensing was found to be highly selective against many other biomolecules including proteins, enzymes, and DNA. Hence, a selective and efficient heparin sensor (FONP-Pro) was developed having a limit of detection of 12 nM simply by utilizing the fluorescence "turn-off" and "turn-on" mechanism of NDI-1 FONP.

Detection of coralyne and heparin by polymerase extension reaction using SYBR Green I

Polydeoxyadenosine (poly (dA)) has been extensively applied for detecting many drug molecules. Herein, we developed a sensitive method for detecting coralyne and heparin using a modified DNA probe with poly (dA) at one end. In the absence of coralyne, the DNA probe was digested by the Exonuclease I (Exo I), and therefore the SYBR Green I (SG I) emitted an extremely low fluorescent signal. While coralyne specifically binding to poly (dA) with strong propensity could remarkably restrain the disintegration of the DNA probe, through which as a template the second strand of DNA sequence was formed with the introduction of DNA polymerase. Therefore, the fluorescent signal of SG I was intensified to quantify coralyne. Based on this method, heparin can be determined due to its strong affinity towards coralyne. This method showed a linear range from 2 to 500 nM for coralyne with a low detection limit of 0.98 nM, and the linear range of heparin was from 1 to 100 nM when 1.25 nm was the detection limit. The proposed method was also implemented successfully in biological samples and showed a potential application for screening potential therapeutic molecules.

Aggregation-Induced Emission Enhancement of CdSe QDs by Protamine and its Application to Sensitively and Selectively Detect Heparin

Background:

Heparin, it is commercially used as an anticoagulant in surgical procedures for the prevention of blood clotting. However, overdose and prolonged use of heparin often induce potentially fatal bleeding complication. So, it is of crucial importance to monitor closely heparin levels for the sake of health. In this work, a sensitive fluorescence sensing platform to detect heparin was set up based on MPA-CdSe QDs (quantum dots) and protamine enhanced fluorescent system.

Methods:

The image of CdSe QDs was taken on a JEM-2100 transmission electron microscope (JEOL Ltd.). The fluorescence spectrum was recorded on a FluoroMax-4 fluorescence spectrophotometer (Horiba, USA). UV–vis absorption spectrum was recorded using a Shimadzu UV-2450 Spectrophotometer (Tokyo, Japan). A vortex mixer IKA MS3 digital was selected to mix the solution.

Results:

Under optimized conditions, the linear response to detect heparin ranges from 0.06 to 14 µg mL-1 with a detection limit of 8 ng mL-1. The approach showed a highly selective response to heparin in the presence of 16 interfered substances.

Conclusion:

A simple method for the detection of heparin was developed based on MPA-CdSe QDs and protamine enhanced fluorescent system. The electrostatic effect between MPA-CdSe QDs and protamine resulted in strong fluorescence enhancement from the MPA-CdSe QDs. Moreover, the addition of heparin could cause a significant fluorescence decrease due to the strong affinity of protamine and heparin. Under optimal conditions, this method displayed a low detection limit and good selectivity over other substances.

Reversible fluorescence modulation of BSA stabilised copper nanoclusters for the selective detection of protamine and heparin

Depicting fluorescence sensing of protamine and heparin based on aggregation and disaggregation of copper nanoclusters.

A ratiometric fluorometric heparin assay based on the use of CdTe and polyethyleneimine-coated carbon quantum dots

CdTe quantum dots (QDs) were integrated with polyethyleneimine-coated carbon dots (PEI-CDs) to form a dually emitting probe for heparin. The red fluorescence of the CdTe QDs is quenched by the PEI-CDs due to electrostatic interactions. In the presence of heparin, the blue fluorescence of PEI-CDs remains unaffected, while its quenching effect on the fluorescence of CdTe QDs is strongly reduced. A ratiometric fluorometric assay was worked out. The ratio of the fluorescences at 595 and 436 nm serves as the analytical signal. Response is linear in the concentration range of 50-600 ng·mL^-1 (0.1-1.2 U·mL^-1) of heparin. The limit of detection is 20 ng·mL^-1 (0.04 U·mL^-1). This makes the method a valuable tool for heparin monitoring during postoperative and long-term care. This assay is relatively free from the interference by other analogues which commonly co-exist with heparin in samples, and it is more robust than single-wavelength based assays. Graphical abstract In the presence of heparin, the fluorescence of polyethyleneimine-coated carbon dots (PEI-CDs) at 436 nm remains unaffected, while its quenching effect on the fluorescence of CdTe at 595 nm is strongly reduced.

A ratiometric detection of heparin with high sensitivity based on aggregation-enhanced emission of gold nanoclusters triggered by silicon nanoparticles

Heparin (Hep) is a widely applied anticoagulant and the quantification of heparin concentration is pivotal for clinical use. In this work, silicon nanoparticles (SiNPs) modified by the amino groups and glutathione-capped gold nanoclusters (GSH-AuNCs) are able to self-assemble into spherical particle structures via the electrostatic interaction, resulting in the aggregation-enhanced emission (AEE) of GSH-AuNCs. However, Hep, a highly sulfated glycosaminoglycan with much more negative charges, can bind with the SiNPs and inhibit the aggregation. As a result, it causes the AEE quenching of GSH-AuNCs at 570 nm but the SiNPs keep their own blue fluorescence at 450 nm. Thus, the SiNPs can act as an internal reference and the GSH-AuNCs are used as a signal probe in this process. The ratiometric fluorescent signal (I₅₇₀/I₄₅₀) change of the nanohybrid probe is positively correlated with Hep concentrations in the range from 6.44 ng/mL to 96.6 ng/mL with the detection limit of 3.29 ng/mL. As expected, this strategy shows good sensitivity and selectivity, and it is also successfully applied to detect Hep in Hep sodium injection and human serum samples with good recoveries.

Fluorometric 'switch-on' detection of heparin based on a system composed of rhodamine-labeled chitosan oligosaccharide lactate, and graphene oxide

A novel fluorescence 'Switch on' for the detection of heparin based on the RhB-COL/GO system was achieved. A strong fluorescence dye, Rhodamine B, was modified by chitosan oligosaccharide lactate (COL), which plays a major role in the formation of a positively charged RhB-COL complex. RhB-COL was soluble and stable in solution, which was characterized by using Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. GO sheets quenched the fluorescence intensity of RhB-COL due to electron transfer from RhB to the GO surface. The decrease in fluorescence intensity of RhB-COL with increasing GO concentration was recorded using a Cary Eclipse fluorescence spectrophotometer. On the other hand, the addition of heparin replaced GO to bind with the RhB-COL surface via an electrostatic and noncovalent bond due to the abundant negative charge, which resulted in recovery of the fluorescence intensity. This RhB-COL/GO system possessed high selectivity and good sensitivity for the detection of heparin compared to other biomolecules, such as glycine, D-glucose, hyaluronic acid, L-glutamic acid, and ascorbic acid. The linear response toward heparin was measured over the range, 0-1.8 U · ml^-1, with a low detection limit of 0.04 U · ml^-1. The satisfactory sensing performance of RhB-COL/GO for heparin supports new 'switch-on' sensor applications in heparin-related biomedical detection.

A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS₂ quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS₂ QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS₂ QD (Adr-CuInS₂ QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H₂O₂, and additionally oxidize the adrenaline to adrenaline quinone. Both the H₂O₂ and the adrenaline quinone can quench the fluorescence of the CuInS₂ QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS₂ QDs. Under the optimum conditions, the fluorescence quenching ratio I_f/I_f0 (I_f and I_f0 were the fluorescence intensity of Adr-CuInS₂ QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10^-8-1 × 10^-4 mol L^-1 with the detection limit of 3.6 nmol L^-1. The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).

Silver triangular nanoplates as an high efficiently FRET donor-acceptor of upconversion nanoparticles for ultrasensitive "Turn on-off" protamine and trypsin sensor

Silver triangular nanoplates (STNPs) as a high efficient fluorescence quenching reagent of upconversion nanoparticles (UCNPs) was used to constract a novel label-free fluorescence nanosensor for ultrasensitive detection of protamine and trypsin based on fluorescence resonance energy transfer (FRET) between STNPs and UCNPs. In this assay, the negatively charged STNPs can bind with positively charged UCNPs through electrostatic interaction, and then quenched the fluorescence of UCNPs. When protamine was added to the mixture of UCNPs-STNPs, the STNPs interacted with protamine and then detached from the surface of UCNPs and aggregated, which result in the recovery of the fluorescence of UCNPs. Trypsin could catalyze the hydrolysis of protamine and effectively quench the fluorescence recovered by protamine. By measuring the changes of the fluorescence of UCNPs, the concentrations of protamine and trypsin were determined. Under the optimized conditions, the linear response range was obtained from 10 to 500ng/mL, 5-80ng/mL and with the low detection limit of 3.1ng/mL and 1.8ng/mL for protamine and trypsin, respectively. Meanwhile, the nanosensor shows good selectivity, sensitivity and can be successfully applied to detection of protamine and trypsin in serum samples.

Gram-Scale Synthesis of Hydrophilic PEI-Coated AgInS2 Quantum Dots and Its Application in Hydrogen Peroxide/Glucose Detection and Cell Imaging

Assisted with polyethylenimine, 4.0 L of water-soluble AgInS₂ quantum dots (AIS QDs) were successfully synthesized in an electric pressure cooker. As-prepared QDs exhibit yellow emission with a photoluminescence (PL) quantum yield up to 32%. The QDs also show excellent water/buffer stability. The highly luminescent AIS QDs are used to explore their dual-functional behavior: detection of hydrogen peroxide (H₂O₂)/glucose and cell imaging. The amino-functionalized AIS QDs show high sensitivity and specificity for H₂O₂ and glucose with detection limits of 0.42 and 0.90 μM, respectively. A linear correlation was established between PL intensity and concentration of H₂O₂ in the ranges of 0.5-10 μM and 10-300 μM, while the linear ranges were 1-10 μM and 10-1000 μM for detection of glucose. The AIS QDs reveal negligible cytotoxicity on HeLa cells. Furthermore, the luminescence of AIS QDs gives the function of optical imaging.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

Single-Particle Ratiometric Pressure Sensing Based on "Double-Sensor" Colloidal Nanocrystals

Ratiometric pressure sensitive paints (r-PSPs) are all-optical probes for monitoring oxygen flows in the vicinity of complex or miniaturized surfaces. They typically consist of a porous binder embedding mixtures of a reference and a sensor chromophore exhibiting oxygen-insensitive and oxygen-responsive luminescence, respectively. Here, we demonstrate the first example of an r-PSP based on a single two-color emitter that removes limitations of r-PSPs based on chromophore mixtures such as different temperature dependencies of the two chromophores, cross-readout between the reference and sensor signals and phase segregation. In our approach, we utilize a novel "double-sensor" r-PSP that features two spectrally separated emission bands with opposite responses to the O₂ pressure, which boosts the sensitivity with respect to traditional reference-sensor pairs. Specifically, we use two-color-emitting dot-in-bulk CdSe/CdS core/shell nanocrystals, exhibiting red and green emission bands from their core and shell states, whose intensities are respectively enhanced and quenched in response to the increased oxygen partial pressure that effectively tunes the position of the nanocrystal's Fermi energy. This leads to a strong and reversible ratiometric response at the single particle level and an over 100% enhancement in the pressure sensitivity. Our proof-of-concept r-PSPs further exhibit suppressed cross-readout thanks to zero spectral overlap between the core and shell luminescence bands and a temperature-independent ratiometric response between 0 and 70 °C.

Fluorescent Strips of Electrospun Fibers for Ratiometric Sensing of Serum Heparin and Urine Trypsin

"Turn-on" or "turn-off" probes remain challenges in the establishment of sensitive, easily operated, and reliable methods for in situ monitoring bioactive substances. In the current study, electrospun fibrous strips are designed to provide straightforward observations of ratiometric color changes with the naked eye in the presence of serum heparin or urine trypsin. A tetraphenylethene (TPE) derivative is constructed and along with phloxine B is grafted on fibers, followed by protamine adsorption to induce static quenching of phloxine B and aggregation-induced emission of the TPE derivative. The presence of heparin or trypsin removes protamine to restore the fluorescence of phloxine B at 574 nm (I₅₇₄) and relieve the emission of the TPE derivative at 472 nm (I₄₇₂). The grafting densities of phloxine B and the TPE derivative are essential to achieve the optimal fluorescence-intensity ratio of I₅₇₄/I₄₇₂ for the ratiometric detection of heparin and trypsin. Under illumination by an ultraviolet lamp, the fibrous mats turn from cyan to green in the presence of heparin at 0.4 U/mL and to a bright yellow at 0.8 U/mL, which is feasible in sensing serum heparin levels during postoperative and long-term care of patients after cardiovascular surgery. The protamine digestion results in similar color transitions with increasing trypsin levels up to 8 μg/mL, indicating the potential for monitoring urine trypsin levels of pancreas transplant patients. The color strips based on the ratiometric fluorescent response indicate advantages in lowering the detection limit and improving the accuracy and reproducibility, bearing great potential for a real-time and naked-eye detection of bioactive substances as self-test devices.

Sensing Active Heparin by Counting Aggregated Quantum Dots at Single-Particle Level

Developing highly sensitive and highly selective assays for monitoring heparin levels in blood is required during and after surgery. In previous studies, electrostatic interactions are exploited to recognize heparin and changes in light signal intensity are used to sense heparin. In the present study, we developed a quantum dot (QD) aggregation-based detection strategy to quantify heparin. When cationic micelles and fluorescence QDs modified with anti-thrombin III (AT III) are added into heparin sample solution, the AT III-QDs, which specifically bind with heparin, aggregate around the micelles. The aggregated QDs are recorded by spectral imaging fluorescence microscopy and differentiated from single QDs based on the asynchronous process of blue shift and photobleaching. The ratio of aggregated QD spots to all counted QD spots is linearly related to the amount of heparin in the range of 4.65 × 10 ^-4 U/mL to 0.023 U/mL. The limit of detection is 9.3 × 10 ^-5 U/mL (∼0.1 nM), and the recovery of the spiked heparin at 0.00465 U/mL (∼5 nM) in 0.1% human plasma is acceptable.

Selective detection of glufosinate using CuInS2 quantum dots as a fluorescence probe

This work designed a fluorescence “turn-off-on” probe to detect glufosinate.

Colorimetric detection of heparin with high sensitivity based on the aggregation of gold nanoparticles induced by polymer nanoparticles

The negatively charged heparin hinders the aggregation of Au nanoparticles induced by the cationic polymer nanodots.

Visual and fluorescence detection of pyrogallol based on a ratiometric fluorescence-enzyme system

Schematic illustration of the synthesis of a CQDs@SiO₂@CdTe QD nanohybrid as a ratiometric fluorescent probe for the detection of PG.

Aggregation-induced emission properties of hydrothermally synthesized Cu–In–S quantum dots

This article reports water-soluble Cu–In–S QDs with aggregation-induced emission (AIE) properties that can be induced by both an organic solvent and cations.

Emissive H-Aggregates of an Ultrafast Molecular Rotor: A Promising Platform for Sensing Heparin

Constructing "turn on" fluorescent probes for heparin, a most widely used anticoagulant in clinics, from commercially available materials is of great importance, but remains challenging. Here, we report the formation of a rarely observed emissive H-aggregate of an ultrafast molecular rotor dye, Thioflavin-T, in the presence of heparin, which provides an excellent platform for simple, economic and rapid fluorescence turn-on sensing of heparin. Generally, H-aggregates are considered as serious problem in the field of biomolecular sensing, owing to their poorly emissive nature resulting from excitonic interaction. To the best of our knowledge, this is the first report, where contrastingly, the turn-on emission from the H-aggregates has been utilized in the biomolecule sensing scheme, and enables a very efficient and selective detection of a vital biomolecule and a drug with its extensive medical applications, i.e., heparin. Our sensor system offers several advantages including, emission in the biologically advantageous red-region, dual sensing, i.e., both by fluorimetry and colorimetry, and most importantly constructed from in-expensive commercially available dye molecule, which is expected to impart a large impact on the sensing field of heparin. Our system displays good performance in complex biological media of serum samples. The novel Thioflavin-T aggregate emission could be also used to probe the interaction of heparin with its only clinically approved antidote, Protamine.