Quantum dots-based ratiometric fluorescence probe for mercuric ions in biological fluids

Highly sensitive and novel dual-emission fluorescence nanosensor utilizing hybrid carbon dots-quantum dots for ratiometric determination of chlorpromazine

Herein, a ratiometric fluorimetric nanosensor is introduced for the sensitive and selective analysis of chlorpromazine (CPZ) via employing blue-emitting B-doped carbon dots (B-CDs) as the reference fluorophore and green-emitting CdTe capped thioglycolic acid (TGA) quantum dots (TGA-CdTe-QDs) as the specific recognition probe. The sensor exhibits dual emission centered at 440 and 560 nm, under a single excitation wavelength of 340 nm. Upon the addition of ultra-trace amount of CPZ, the fluorescence signal of TGA-CdTe-QDs declines due to electron transfer process from excited TGA-CdTe-QDs to CPZ molecules, whereas the fluorescence peak of B-CDs is unaffected. Therefore, a new fluorimetric platform was prepared for the assay of CPZ in the range of 2.2 × 10-10 to 5.0 × 10-9 M with a detection limit of 1.3 × 10-10 M. Moreover, the practicability of the designed strategy was investigated for the detection of CPZ in biological samples and the results demonstrate that it possesses considerable potential to be utilized in practical applications.

Ratiometric fluorescent sensing of melatonin based on inner filter effect and smartphone established detection

Melatonin (MLT) is a crucial neurohormone having inhibitory effects over various types of cancer. In this work, 3,6-Diaminocarbazole (DAC), a fluorescent probe is utilized to detect MLT in a highly sensitive, selective and facile way. The unique feature of present work is that MLT is sensed by ratiometric fluorescent technique based on the inner filter effect (IFE) using DAC at an emission wavelength of 310 nm. As a result, a noticeable change in color from red to cyan is observed and the quantitative analysis of fluorescence signals at these wavelengths are used to detect MLT observing a linear relationship between the ratio of emission intensities and the concentration of MLT over a linear range of 0 to 78 μM. DAC can accurately measure the detailed quantity of MLT with a limit of detection of 30 nM and has proved to be an efficient sensing probe due to its excellent molar absorptivity and high photoluminescence quantum yield (PLQY). Sensing characterization was carried out UV-Vis, steady-state, and time- resolved fluorescence spectroscopic techniques. The smartphone app "RGB colour detector" value has been successfully linked with the considerable detectable color changes of DAC on addition of MLT. HOMO-LUMO have been calculated using DFT with B3LYP/6-31G(d,p) level and band gaps of 3.77 eV and 4.91 eV were found for DAC and MLT, respectively. Electrons are not allowed energetically to transfer from MLT to DAC, as is evident from their band gaps. Therefore, IFE can be considered the foremost method in fluorescence quenching of present investigation. The developed sensor was verified by spiking of MLT in human serum.

In-situ quantification of lipids in live cells through imaging approaches

Lipids are important molecules that are widely distributed within the cell, and they play a crucial role in several biological processes such as cell membrane formation, signaling, cell motility and division. Monitoring the spatiotemporal dynamics of cellular lipids in real-time and quantifying their concentrations in situ is crucial since the local concentration of lipids initiates various signaling pathways that regulate cellular processes. In this review, we first introduced the historical background of lipid quantification methods. We then delve into the current state of the art of in situ lipid quantification, including the establishment and utility of fluorescence imaging techniques based on sensors of lipid-binding domains labeled with organic dyes or fluorescent proteins, and Raman and magnetic resonance imaging (MRI) techniques that do not require lipid labeling. Next, we highlighted the biological applications of live-cell lipid quantification techniques in the study of in situ lipid distribution, lipid transformation, and lipid-mediated signaling pathways. Finally, we discussed the technical challenges and prospects for the development of lipid quantification in live cells, with the aim of promoting the development of in situ lipid quantification in live cells, which may have a profound impact on the biological and medical fields.

Double-Emission Ratiometric Fluorescent Sensors Composed of Rare-Earth-Doped ZnS Quantum Dots for Hg2+ Detection

Quantum dots (QDs) are a class of zero-dimensional nanocrystal materials, whose lengths are limited to 2-10 nm. Their unique advantages such as wide excitation spectra, narrow emission spectra, and high quantum yield make their application possible in fluorescence sensing, wherein QDs such as CdSe, CdTe, and CdS are used. Indeed, QDs have a wide range of applications in fluorescence sensing, and there have been many reports of applications based on QDs as ion probes. The emission spectra of QDs can be adjusted by changing the size of the QDs or doping them with other ions/elements. However, the high toxicity of Cd and the poor anti-interference ability of single-emission fluorescent probes greatly limit the applications of QDs in many fields. In this paper, ZnS QDs are doped with the rare-earth element Ce to form a low-toxicity double-emission ratiometric fluorescent sensor, ZnS:Ce, for Hg²⁺ detection. The results of transmission electron microscopy (TEM), X-ray diffractometry, X-ray photoelectron spectroscopy, and optical spectroscopy show that ZnS:Ce QDs were successfully synthesized. Under the optimal conditions, the concentration of Hg²⁺ was in the range of 10-100 μM, which had a linear relationship with the fluorescence intensity of the ZnS:Ce QDs: the linear correlation coefficient was 0.998, and the detection limit was 0.82 μM L^-1. In addition, the fluorescent sensor had good selectivity for Hg²⁺, and it was successfully applied to the detection of Hg²⁺ in laboratory water samples.

FRET probe for selective and sensitive detection of vitamin A by cadmium free quantum dots (ZnS)

Vitamin A as a powerful antioxidant plays an important role in human body functions including bone remodeling regulation, healthy immune system and cell growth reproduction. An accurate determination of vitamin A is taken into consideration because of its importance for human health. In this paper, we reported a fluorescence resonance energy transfer (FRET) probe, MPS-capped ZnS QDs, for sensitive and selective detection of vitamin A. The colloidal MPS-capped ZnS QDs were prepared from Zinc acetate and sodium sulfide by employing 3-mercaptopropyltrimethoxysilane (MPS) molecules as the stabilizer or capping agent at the pH condition of 10. The synthesized MPS-capped ZnS QDs were characterized by means of FT-IR, UV-Vis, DLS, and TEM techniques. The sensing behavior of MPS-capped ZnS QDs for selective and sensitive detection of vitamin A, vitamin B₂, vitamin B₆, vitamin E, vitamin K, vitamin H, vitamin D₃ and vitamin C was investigated using fluorescence spectroscopy. The detection mechanism involves photoinduced charge transfer from the surface of ZnS QDs to Vitamin resulting in the fluorescence quenching of ZnS QDs followed by nonradiative fluorescence resonance energy transfer. An excellent selectivity was observed for vitamin A versus other tested species. A linear relationship was observed between the fluorescence intensity of MPS-capped ZnS QDs and the concentration of vitamin A in the range of 3.33-36.66 μM with detection limit of 1.062 μM.

Controllable and robust dual-emissive quantum dot nanohybrids as inner filter-based ratiometric probes for visualizable melamine detection

The ratiometric fluorescence technique is of great interest due to its visualization characteristics. The construction of a reliable fluorescent ratiometric nanoprobe for high-sensitivity visual quantification is highly sought after but it is limited by poor stability and controllability. Herein, we report a robust dual-emissive quantum dot nanohybrid with precise color tunability and demonstrate its potential as a two-signal-change ratiometric probe for visual detection. A novel assembly strategy was developed for spatially implanting hydrophobic green and red quantum dots (QDs) into a silica scaffold to form a dual-emissive hierarchical fluorescent silica nanohybrid. The fluorescence intensity ratio and color of the nanohybrid were precisely tailored by altering the amounts of green and red QDs. Particularly, after the alkylsilane-mediated phase transfer and exterior silica shell growth, the nanohybrid exhibited the well-preserved fluorescence features of the original QDs and robust optical/colloid stability. An inner filter-based ratiometric nanoprobe for the visual determination of melamine was ultimately devised by combining the spectra-overlapped two-colored fluorescent nanohybrid with analyte-specific gold nanoparticles. Furthermore, based on the reversible fluorescence signal changes in two-colored QDs induced by melamine, a logic gate strategy for melamine monitoring was constructed. The newly developed fluorescent ratiometric nanoprobe shows great prospects for the visual and quantitative determination of analytes in a complex biological matrix.

Carbon dot-based fluorometric optical sensors: an overview

Fluorescent carbon dots (CDs) are a new class of carbon nanomaterials and have demonstrated excellent optical properties, good biocompatibility, great aqueous solubility, low cost, and simple synthesis. Since their discovery, various synthesis methods using different precursors were developed, which were mainly classified as top-down and bottom-up approaches. CDs have presented many applications, and this review article mainly focuses on the development of CD-based fluorescent sensors. The sensing mechanisms, sensor design, and sensing properties to various targets are summarized. Broad ranges of detection, including temperature, pH, DNA, antibiotics, cations, cancer cells, and antibiotics, have been discussed. In addition, the challenges and future directions for CDs as sensing materials are also presented.

Ratiometric fluorescent nanoprobes for visual detection: Design principles and recent advances - A review

Signal generation techniques for visual detection of analytes have received a great deal of attention in various sensing fields. These approaches are considered to be advantageous when instrumentation cannot be employed, such as for on-site assays, point-of-care tests, and he althcare diagnostics in resource-constrained areas. Amongst various visual detection approaches explored for non-invasive quantitative measurements, ratiometric fluorescence sensing has received particular attention as a potential method to overcome the limitations of intensity-based probes. This technique relies on changes in the intensity of two or more emission bands (induced by an analyte), resulting in an effective internal referencing which improves the sensitivity of the detection. The self-calibration, together with the unique optophysical properties of nanoparticles (NPs) have made the ratiometric fluorescent nanoprobes more sensitive and reliable, which in turn, can result in more precise visual detection of the analytes. Over the past few years, a vast number of ratiometric sensing probes using nanostructured fluorophores have been designed and reported for a wide variety of sensing, imaging, and biomedical applications. In this work, a review on the NP-based ratiometric fluorescent sensors has been presented to meticulously elucidate their development, advances and challenges. With a special emphasis on visual detection, the most important steps in the design of fluorescent ratiometric nanoprobes have been given and based on different classes of analytes, recent applications of fluorescent ratiometric nanoprobes have been summarized. The challenges for the future use of the technique investigated in this review have been also discussed.

Hydroxyl phenyl imino modified phenanthro[9,10-d] imidazole: An AIEE-active sensor for determination of Cu2+ in water samples and subsequent "turn-on" recognition of Cr3+ with logic gates

A 2-hydroxyl phenyl imino modified phenanthro[9,10-d]imidazole probe (PPIP) was synthesized and its aggregation-induced emission enhancement (AIEE) phenomenon in aqueous medium was characterized by the Tyndall phenomena, morphologies of scanning electron microphotograph (SEM) as well as the enhanced fluorescence intensities. The AIEE-active PPIP in aggregated states exhibited a sensitive detection for Cu²⁺ along with the elimination of fluorescence intensity; subsequently, in situPPIP-Cu²⁺ complex showed selective fluorescence "turn-on" for Cr³⁺, providing a potential platform for tandem recognition of Cu²⁺ and Cr³⁺. The 1:1 M ratio between PPIP and Cu²⁺ was confirmed by Job's plot, ¹H NMR spectra, mass spectra and density functional theory (DFT) calculations. The detection limits for Cu²⁺ and Cr³⁺ were 4.127 × 10^-2 μM and 9.404 × 10^-1 μM, respectively. Moreover, this successive recognition could be utilized to construct the molecular logic gates by the fluorescence changes. In addition, PPIP was successfully employed for quantitative detecting Cu²⁺ in real water samples with satisfactory results.

Isocyanonaphthalenes as extremely low molecular weight, selective, ratiometric fluorescent probes for Mercury(II)

The specially designed chemical structure of our recently developed solvatochromic amino-isocyanonaphthalene (ICAN) dye family enables the selective detection of Hg²⁺ and at the same time is able to indicate the presence of Ag⁺. In addition to its easy preparation and nontoxic nature, ICAN is the lowest molecular weight dye reported for ratiometric fluorescent Hg²⁺ detection in water, so far. The basis of this double selectivity is the reduction of the isonitrile moiety to amine by a chemical reaction with Hg²⁺ resulting in a greater than 100 nm hypsochromic shift (and switch on of fluorescence) of the emission maximum relative to ICAN, whereas the complexation of Ag⁺ with the NC group yields an approximately 20 nm bathochromic shift (and quenching). In contrast, other common ions have little effect on the position of the emission maximum in aqueous medium. In completely aqueous medium at pH = 6, the limit of quantification was found to be lower than 17 nM and the limit of detection lower than 6 nM for Hg²⁺. The practical applicability of the method was demonstrated on dental amalgam.

Sensing with photoluminescent semiconductor quantum dots

Fluorescent sensors benefit from high signal-to-noise and multiple measurement modalities, enabling a multitude of applications and flexibility of design. Semiconductor nanocrystal quantum dots (QDs) are excellent fluorophores for sensors because of their extraordinary optical properties. They have high thermal and photochemical stability compared to organic dyes or fluorescent proteins and are extremely bright due to their large molar cross-sections. In contrast to organic dyes, QD emission profiles are symmetric, with relatively narrow bandwidths. In addition, the size tunability of their emission color, which is a result of quantum confinement, make QDs exceptional emitters with high color purity from the ultra-violet to near infrared wavelength range. The role of QDs in sensors ranges from simple fluorescent tags, as used in immunoassays, to intrinsic sensors that utilize the inherent photophysical response of QDs to fluctuations in temperature, electric field, or ion concentration. In more complex configurations, QDs and biomolecular recognition moieties like antibodies are combined with a third component to modulate the optical signal via energy transfer. QDs can act as donors, acceptors, or both in energy transfer-based sensors using Förster resonance energy transfer (FRET), nanometal surface energy transfer (NSET), or charge or electron transfer. The changes in both spectral response and photoluminescent lifetimes have been successfully harnessed to produce sensitive sensors and multiplexed devices. While technical challenges related to biofunctionalization and the high cost of laboratory-grade fluorimeters have thus far prevented broad implementation of QD-based sensing in clinical or commercial settings, improvements in bioconjugation methods and detection schemes, including using simple consumer devices like cell phone cameras, are lowering the barrier to broad use of more sensitive QD-based devices.

Ratiometric fluorescence sensing of mercuric ion based on dye-doped lanthanide coordination polymer particles

This work focused on the development of a novel ratiometric fluorescence sensor for detection of Hg²⁺ by using dye-doped lanthanide infinite coordination polymer (Ln-ICP) particles. The dye-doped Ln-ICP used herein was prepared by self-assemble of adenosine monophosphate (AMP) with Ce³⁺ and Tb³⁺ (Ce/Tb-AMP) through self-adaptive chemistry, in which the fluorescent dye coumarin was encapsulated during the assembly process as a guest molecule. Under 310 nm irradiation, the obtained coumarin@Ce/Tb-AMP itself emitted characteristic green luminescence of Tb³⁺, accompanied with a weak fluorescence at 445 nm originated from coumarin encapsulated in the Ce/Tb-AMP networks. The fluorescence emission of coumarin became strong when it was released to the solution. In the presence of Hg²⁺, the coumarin@Ce/Tb-AMP was destroyed due to the specific coordination interaction between AMP and Hg²⁺, which leaded to the release of coumarin to the solution meanwhile. Consequently, the fluorescence of Ce/Tb-AMP was quenched, while that of coumarin enhanced. On the basis of this strategy, we developed a novel ratiometric fluorescent sensor for the detection of Hg²⁺ by measuring the ratio of fluorescent intensity of the coumarin@Ce/Tb-AMP suspension, which showed a wide linear range from 0.08 to 1000 nM and detection limit of 0.03 nM with high selectivity and sensitivity. Furthermore, the constructed ratiometric fluorescent sensor was successfully applied in detecting Hg²⁺ in drinking water and human blood serum (HBS) with satisfactory results.

Dual-emission ratiometric fluorescence detection of aspirin in human saliva: onsite naked-eye detection and high stability

A highly stable ratiometric fluorescence probe based on dual-emission QDs was designed for the visual detection of aspirin in human saliva.

Fabrication of an "ion-imprinting" dual-emission quantum dot nanohybrid for selective fluorescence turn-on and ratiometric detection of cadmium ions

In this work, we have fabricated a new dual-emission quantum dot (QD) nanohybrid for fluorescence ratiometric determination of cadmium ions (Cd²⁺) in water samples, where the "turn-on" model and "ion-imprinting" technique were incorporated simultaneously. The nanohybrid probe was composed of green-emitting CdSe QDs covalently linked onto the surface of silica nanoparticles embedded with red-emitting CdTe QDs. The chemical etching of ethylene diamine tetraacetic acid (EDTA) at the surface produced specific Cd²⁺ recognition sites and quenched the green fluorescence of outer CdSe QDs. Upon exposure to different amounts of Cd²⁺, the green fluorescence was gradually restored, whereas the inner red fluorescence remained constant. As a consequence, an obviously distinguishable fluorescence color variation (from red to green) of the probe solution was observed. Under the optimized conditions, the developed ratiometric sensor displayed a linear response range from 0.1 to 9 μM with a detection limit of 25 nM (S/N = 3) for Cd²⁺, which could offer an alternative sensing approach for the highly sensitive and selective detection of heavy metal ions.

Efficient Detection of Trace Hg²⁺ in Water Based on the Fluorescence Quenching of Environment-friendly Thiol-functionalized Poly(vinyl alcohol) Capped CdS Quantum Dots Nanocomposite

Using environment-friendly materials for sensing toxic metal ions has drawn significant attention in recent research. Herein, we present an aqueous synthesis of stable CdS quantum dots (QDs) using thiol-functionalized poly(vinyl alcohol) (PVA) as the unique capping ligand for the detection of trace Hg(2+) in environmental water samples. The CdS QDs with an average size of 3.3 nm had good water-solubility and favorable fluorescence with a quantum yield of 32.8% and a longer luminescence lifetime of 31.9 ns. The fluorescence intensity of QDs aqueous solution in the 520 nm wavelength was quenched upon the addition of Hg(2+). Under the optimal conditions, the ratio of the blank fluorescence intensity to the quenched fluorescence intensity was linearly proportional to the Hg(2+) concentration from 2 to 4000 nM with a detection limit of 1 nM. Also, many co-existing metal ions were not interfered with the detection of Hg(2+). This nanomaterial was successfully applied to the measurement of Hg(2+) in water samples.

Fluorescent nanoprobes for sensing and imaging of metal ions: recent advances and future perspectives

Recent advances in nanoscale science and technology have generated nanomaterials with unique optical properties. Over the past decade, numerous fluorescent nanoprobes have been developed for highly sensitive and selective sensing and imaging of metal ions, both in vitro and in vivo. In this review, we provide an overview of the recent development of the design and optical properties of the different classes of fluorescent nanoprobes based on noble metal nanomaterials, upconversion nanoparticles, semiconductor quantum dots, and carbon-based nanomaterials. We further detail their application in the detection and quantification of metal ions for environmental monitoring, food safety, medical diagnostics, as well as their use in biomedical imaging in living cells and animals.

Ratiometric fluorescence, electrochemiluminescence, and photoelectrochemical chemo/biosensing based on semiconductor quantum dots

Ratiometric fluorescent sensors, which can provide built-in self-calibration for correction of a variety of analyte-independent factors, have attracted particular attention for analytical sensing and optical imaging with the potential to provide a precise and quantitative analysis. A wide variety of ratiometric sensing probes using small fluorescent molecules have been developed. Compared with organic dyes, exploiting semiconductor quantum dots (QDs) in ratiometric fluorescence sensing is even more intriguing, owing to their unique optical and photophysical properties that offer significant advantages over organic dyes. In this review, the main photophysical mechanism for generating dual-emission from QDs for ratiometry is discussed and categorized in detail. Typically, dual-emission can be obtained either with energy transfer from QDs to dyes or with independent dual fluorophores of QDs and dye/QDs. The recent discovery of intrinsic dual-emission from Mn-doped QDs offers new opportunities for ratiometric sensing. Particularly, the signal transduction of QDs is not restricted to fluorescence, and electrochemiluminescence and photoelectrochemistry from QDs are also promising for sensing, which can be made ratiometric for correction of interferences typically encountered in electrochemistry. All these unique photophysical properties of QDs lead to a new avenue of ratiometry, and the recent progress in this area is addressed and summarized here. Several interesting applications of QD-based ratiometry are presented for the determination of metal ions, temperature, and biomolecules, with specific emphasis on the design principles and photophysical mechanisms of these probes.

Ratiometric fluorescent paper sensor utilizing hybrid carbon dots-quantum dots for the visual determination of copper ions

A simple and effective ratiometric fluorescence nanosensor for the selective detection of Cu(2+) has been developed by covalently connecting the carboxyl-modified red fluorescent cadmium telluride (CdTe) quantum dots (QDs) to the amino-functionalized blue fluorescent carbon nanodots (CDs). The sensor exhibits the dual-emissions peaked at 437 and 654 nm, under a single excitation wavelength of 340 nm. The red fluorescence can be selectively quenched by Cu(2+), while the blue fluorescence is a internal reference, resulting in a distinguishable fluorescence color change from pink to blue under a UV lamp. The detection limit of this highly sensitive ratiometric probe is as low as 0.36 nM, which is lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, a paper-based sensor has been prepared by printing the hybrid carbon dots-quantum dots probe on a microporous membrane, which provides a convenient and simple approach for the visual detection of Cu(2+). Therefore, the as-synthesized probe shows great potential application for the determination of Cu(2+) in real samples.

A Novel Ratiometric Probe Based on Nitrogen-Doped Carbon Dots and Rhodamine B Isothiocyanate for Detection of Fe(3+) in Aqueous Solution

A ratiometric probe for determining ferric ions (Fe(3+)) was developed based on nitrogen-doped carbon dots (CDs) and rhodamine B isothiocyanate (RhB), which was then applied to selective detection of Fe(3+) in PB buffer solution, lake water, and tap water. In the sensing system, FePO4 particles deposit on the surface of CDs, resulting in larger particles and surface passivation. The fluorescence (FL) intensity and the light scattering (LS) intensity of CDs can be gradually enhanced with the addition of Fe(3+), while the FL intensity of RhB remains constant. The ratiometric light intensity of CDs LS and RhB FL was quantitatively in response to Fe(3+) concentrations in a dynamic range of 0.01-1.2 μM, with a detection limit as low as 6 nM. Other metal ions, such as Fe(2+), Al(3+), K(+), Ca(2+), and Co(2+), had no significant interference on the determination of Fe(3+). Compared with traditional probes based on single-signal probe for Fe(3+) detection, this dual-signal-based ratiometric probe exhibits a more reliable and stable response on target concentration and is characterized by easy operation in a simple fluorescence spectrophotometer.

Controlled synthesis of a dual-emission hierarchical quantum dot hybrid nanostructure as a robust ratiometric fluorescent sensor

A highly stable and biocompatible CdTe@SiO₂@CdTe@SiO₂ dual-emission hierarchical hybrid nanostructure was synthesized and used as a robust ratiometric fluorescent sensor.

QD-Based FRET Probes at a Glance

The unique optoelectronic properties of quantum dots (QDs) give them significant advantages over traditional organic dyes, not only as fluorescent labels for bioimaging, but also as emissive sensing probes. QD sensors that function via manipulation of fluorescent resonance energy transfer (FRET) are of special interest due to the multiple response mechanisms that may be utilized, which in turn imparts enhanced flexibility in their design. They may also function as ratiometric, or "color-changing" probes. In this review, we describe the fundamentals of FRET and provide examples of QD-FRET sensors as grouped by their response mechanisms such as link cleavage and structural rearrangement. An overview of early works, recent advances, and various models of QD-FRET sensors for the measurement of pH and oxygen, as well as the presence of metal ions and proteins such as enzymes, are also provided.

Dual-emission fluorescent sensor based on AIE organic nanoparticles and Au nanoclusters for the detection of mercury and melamine

A novel dual-emission ratiometric fluorescence probe is designed and developed by linking two parts, positively charged aggregation-induced emission (AIE) organic fluorescence nanoparticles (OFNs) as the reference and negatively charged Au nanoclusters (Au NCs) as the response, by electrostatic attraction for the first time. This probe can be used for not only visual but quantitative determination of Hg(2+) as well as melamine, because red fluorescence of Au NCs can be quenched by mercury ions and recovered by melamine, due to the strong affinity metallophilic Hg(2+)-Au interaction and stronger affinity Hg(2+)-N. During this process, the green fluorescence of AIE-OFNs remains constant owing to the protection of ε-polylysine (ε-Ply). In addition, the prepared dual-emission ratiometric fluorescence probe has good biocompatibility, indicating the potential of the probe in applications of biological imaging and detection. The results revealed that this dual-emission ratiometric fluorescence probe broadens the application of AIE-based organic fluorescent nanoparticles, and presents a new method to prepare more sensitive, biocompatible, and visual ratiometric fluorescent probes.

Highly sensitive and selective detection of mercury ions based on up-conversion FRET from NaYF4:Yb3+/Er3+ nanophosphors to CdTe quantum dots

The detection of Hg²⁺ has attracted considerable attention because of the serious health and environmental problems caused by it.

Mn-doped ZnS quantum dots with a 3-mercaptopropionic acid assembly as a ratiometric fluorescence probe for the determination of curcumin

Mn-doped ZnS quantum dots capped with 3-mercaptopropionic acid (MPA) were synthesized by a facile method in aqueous solution as a ratiometric fluorescent (I_{590 nm}/I_{458 nm}) probe for curcumin.

Recent progress in quantum dot based sensors

Recent progress in quantum dot (QD) based chemo- and biosensors for various applications is summarized.