Near-infrared fluorescence probe for the determination of acid phosphatase and imaging of prostate cancer cells

Development of a fluorometric and colorimetric dual-mode sensing platform for acid phosphatase assay based on Fe3+ functionalized CuInS2/ZnS quantum dots

BACKGROUND

The spectral dual-mode response towards analyte has been attracted much attention, benefiting from the higher detection accuracy of such strategy in comparison to single signal readout. However, the currently reported dual-mode sensors for acid phosphatase (ACP) activity are still limited, and most of them more or less exist some deficiencies, such as complicated construction procedure, high-cost, poor biocompatibility, aggregation-caused quenching and limited emission capacity.

RESULTS

Herein, we employed Fe3+ functionalized CuInS2/ZnS quantum dots (CIS/ZnS QDs) as nanosensor to develop a novel fluorometric and colorimetric dual-mode assay for ACP activity, combing with ACP-triggered hydrolysis of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA). The Fe3+ binding to CIS/ZnS QDs can be reduced into Fe2+ during the determination, resulting in the dramatically weakened photoinduced electron transfer (PET) effect and the disappearance of competition absorption. Thus, a highly sensitive ACP assay in the range of 0.22-12.5 U L-1 through fluorescence "turn-on" mode has been achieved with a detection of limit (LOD) of 0.064 U L-1. Meanwhile, the ACP activity can also be quantified by spectrophotometry based on the chromogenic reaction of the formed Fe2+ with 1,10-phenanthroline (Phen). Moreover, the designed nanosensor with good biocompatibility was successfully applied to image and monitor the ACP levels in living cells.

SIGNIFICANCE

We believe that the proposed method has remarkable advantages and potential application for ACP assay in terms of the high accuracy, simplicity, low cost, as well as its adequate sensitivity.

Adjustable luminescence copper nanoclusters nanoswitch based on competitive coordination of samarium ions for cascade detection of adenosine triphosphate and acid phosphatase activity

Benefit from the strong coordination property, lanthanide metal ions have been used as competitive reagents to modulate the fluorescence changes of the system. However, lanthanide metal ions as inducers for aggregation-induced emission enhancement in nanosystems is rare. Herein, we report a "turn on-off-on" fluorescent switch for cascade detection of acid phosphatase (ACP) and adenosine triphosphate (ATP) based on the competitive coordination of samarium ions (Sm3+). Novel copper nanoclusters (CuNCs) with long wavelength emission (614 nm) stabilized by glutathione (GSH) and glycylglycine (Gly-Gly) have been confirmed to have AIE property. With the continuous aggregation of GSH/Gly-Gly CuNCs under the induction of Sm3+, the fluorescence of the system increased to achieve the "turn-on" process. The coordinated behaviour between Sm3+ and GSH/Gly-Gly CuNCs is discussed. Due to the strong metal coordination ability of ATP, the Sm3+ coordinated with the GSH/Gly-Gly CuNCs is competed out, resulting in the fluorescence "turn-off" process of the system. As the substrate of enzymatic hydrolysis of ACP, with the continuous hydrolysis of ATP by ACP, Sm3+ coordinates with GSH/Gly-Gly CuNCs again, which leads to the AIE effect and realize the fluorescence "turn-on" process of the system. This strategy results in ATP linear range of 0.508 ~ 120.0 μM with a detection limit of 0.508 μM (S/N = 3) and ACP linear range of 0.011 ~ 30.0 U·L-1 with a detection limit of 0.011 U·L-1 (S/N = 3). Application to biologic samples was successful.

A dual-emission ratiometric fluorescent sensor based on copper nanoclusters encapsulated in zeolitic imidazolate framework-90 for rapid detection and imaging of adenosine triphosphate

Adenosine triphosphate (ATP) is the primary energy carrier for intracellular metabolic processes. Accurate and rapid detection of ATP has important implications for clinical diagnosis. In this work, we reported a dual-emission ratiometric fluorescent probe Cu NCs-Al@ZIF-90 formed by encapsulating copper nanoclusters (Cu NCs) into zeolitic imidazolate framework-90 (ZIF-90) using a simple one-pot method. Cu NCs exhibited a remarkable fluorescence enhancement in the presence of aluminum ions due to the aggregation-induced emission (AIE) properties. When ATP existed, the Zn²⁺ nodes in the MOF material acted as selective sites for ATP recognition, resulting in the cleavage of Cu NCs-Al@ZIF-90. As a consequence, two reverse fluorescence changes were observed from released Cu NCs at 620 nm and imidazole-2-carboxaldehyde (2-ICA) at 450 nm, respectively. With the dual-emission ratiometric strategy, efficient and rapid determination of ATP was realized, giving a detection limit down to 0.034 mM in the concentration range of 0.2 mM to 0.625 mM. The convenient synthesis process and the rapid ATP-responsive ability made the proposed Cu NCs-Al@ZIF-90 probe highly promising in clinical and environmental analysis.

Green- and Red-Emitting Fluorescent Silicon Nanoparticles: Synthesis, Mechanism, and Acid Phosphatase Sensing

Until now, the green and facile synthesis of multicolor fluorescent silicon nanoparticles (SiNPs) with favorable biocompatibility for cellular imaging and biosensors is still a challenge. Herein, a facile one-step room temperature method for preparing fluorescent SiNPs displayed different emission wavelengths was reported. Green and red fluorescent SiNPs (G-SiNPs and R-SiNPs) were synthesized by adjusting the concentration of the reducing agent 2,4-diaminophenol hydrochloride when the amount of N-[3-(trimethoxysilyl)-propyl]-ethylenediamine was consistent. Characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, the results revealed that the G-SiNPs and R-SiNPs were assembled by polymerization of different building blocks, and the emission characteristics of these SiNPs were attributed to the difference in their structural composition and particle size. Interestingly, these fluorescent SiNPs exhibited excellent water solubility, salt tolerance, pH stability, photobleaching resistance, and low cytotoxicity, which facilitated multicolor cell imaging, and further led to these SiNPs were highly attractive in a variety of applications, such as multi-channel sensing and biological imaging. Furthermore, the R-SiNPs have shown the potential to detect acid phosphatase, which is a biomarker of prostate cancer.

A feasible self-assembled near-infrared fluorescence sensor for acid phosphatase detection and cell imaging

The single signal amplification strategy is significant for detecting various disease biomarkers but is restricted by its limited accuracy. The multi-signal and multi-mode methods have overcome this deficiency. Acid phosphatase (ACP) is an important intracellular enzyme but one-step cell imaging material-based probes are scarce for ACP. Herein, we designed a one-step self-assembled polymer probe using neutral red (NR), modified-(pyridoxal-5'-phosphate (PLP)) and Eu³⁺. The polymer exhibited non-emission and excellent stability. Upon the catalytic hydrolysis reaction of ACP, the polymer exhibited two strong fluorescence signals at 373 nm and 613 nm and an appreciable decline of absorbance at 395 nm. The probe has excellent selectivity and higher sensitivity with a limit of detection as low as 0.02 mU mL^-1. It possesses favorable biocompatibility and has been successfully used to detect and image intracellular ACP in several living cells.

Luminescent copper indium sulfide (CIS) quantum dots for bioimaging applications

Copper indium sulfide (CIS) quantum dots are ideal for bioimaging applications, by being characterized by high molar absorption coefficients throughout the entire visible spectrum, high photoluminescence quantum yield, high tolerance to the presence of lattice defects, emission tunability from the red to the near-infrared spectral region by changing their dimensions and composition, and long lifetimes (hundreds of nanoseconds) enabling time-gated detection to increase signal-to-noise ratio. The present review collects: (i) the most common procedures used to synthesize stable CIS QDs and the possible strategies to enhance their colloidal stability in aqueous environment, a property needed for bioimaging applications; (ii) their photophysical properties and parameters that affect the energy and brightness of their photoluminescence; (iii) toxicity and bioimaging applications of CIS QDs, including tumor targeting, time-gated detection and multimodal imaging, as well as theranostics. Future perspectives are analyzed in view of advantages and potential limitations of CIS QDs compared to most traditional QDs.

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.

Smartphone colorimetric assay of acid phosphatase based on a controlled iodine-mediated etching of gold nanorods

A simple but efficient colorimetric assay was developed for the detection and quantification of acid phosphatase (ACP) using a smartphone. This strategy is based on target-controlled iodine-mediated etching of gold nanorods (AuNRs). Due to effective hydrolysis of the substrate pyrophosphate (PPi) by ACP, chelated Cu²⁺ with PPi was released, which promoted the redox reaction with an iodide ion (I^-), leading to the formation of I₃^-. As the etching agent of AuNRs, I₃^- caused a blueshift of the localized surface plasmon resonance peak and, more importantly, an observable color change. The vivid colors were recorded with a smartphone camera and directly analyzed using an image-processing app. On the basis of the direct correlation between ACP concentration and the etching degree of AuNRs as well as color change, this smartphone nanocolorimetry technique showed a good linear response toward ACP over the range of 0-15.0 U/L, with a detection limit of 0.97 U/L. Using the standard addition method, the practical applicability of the proposed smartphone-based assay was successfully demonstrated by determining ACP in human serum samples, with results consistent with those obtained by UV-Vis spectrophotometry.

A lysosome-targeted near-infrared fluorescent probe for imaging of acid phosphatase in living cells

Fluorescent probes for the detection of acid phosphatases (ACP) are important in the investigation of the pathology and diagnosis of diseases. We reported a lysosome-targeted near-infrared (NIR) fluorescent probe SHCy-P based on a novel NIR-emitting thioxanthene-indolium dye for the detection of ACP. The probe showed a long wavelength fluorescence emission at λ_em = 765 nm. Due to the ACP-catalyzed cleavage of the phosphate group in SHCy-P, the probe exhibited high selectivity and sensitivity for the 'turn-on' detection of ACP with a limit of detection as low as 0.48 U L^-1. The probe SHCy-P could also be used to detect and image endogenous ACP in lysosomes. In light of these prominent properties, we envision that SHCy-P will be an efficient optical imaging approach for investigating the ACP activity in disease diagnosis.

Rational Design of High-Performance Donor-Linker-Acceptor Hybrids Using a Schiff Base for Enabling Photoinduced Electron Transfer

Donor-linker-acceptor (D-L-A)-based photoinduced electron transfer (PET) has been frequently used for the construction of versatile fluorescent chemo/biosensors. However, sophisticated and tedious processes are generally required for the synthesis of these probes, which leads to poor design flexibility. In this work, by exploiting a Schiff base as a linker unit, a covalently bound D-L-A system was established and subsequently utilized for the development of a PET sensor. Cysteamine (Cys) and N-acetyl-l-cysteine (NAC) costabilized gold nanoclusters (Cys/NAC-AuNCs) were synthesized and adopted as an electron acceptor, and pyridoxal phosphate (PLP) was selected as an electron donor. PLP can form a Schiff base (an aldimine) with the primary amino group of Cys/NAC-AuNC through its aldehyde group and thereby suppresses the fluorescence of Cys/NAC-AuNC. The Rehm-Weller formula results and a HOMO-LUMO orbital study revealed that a reductive PET mechanism is responsible for the observed fluorescence quenching. Since the pyridoxal (PL) produced by the acid phosphatase (ACP)-catalyzed cleavage of PLP has a weak interaction with Cys/NAC-AuNC, a novel turn-on fluorescent method for selective detection of ACP was successfully realized. To the best of our knowledge, this is the first example of the development of a covalently bound D-L-A system for fluorescent PET sensing of enzyme activity based on AuNC nanoprobes using a Schiff base.

Engineering Two-Dimensional Pd Nanoplates with Exposed Highly Active {100} Facets Toward Colorimetric Acid Phosphatase Detection

Enzyme-like activity and efficiency of nanomaterials are strongly controlled by their size, composition, and structure, and hence the structural parameters need to be optimized. Here, we report that two-dimensional Pd nanoplates enclosed by {100}-facets [{100}PdSP@rGO] exhibit substantially enhanced intrinsic oxidase-like activities relative to the {111}-facets ones and Pd nanocubes in catalyzing the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine. By taking ascorbic acid 2-phosphate as the substrate, which transforms to ascorbic acid in the presence of acid phosphatase (ACP), the {100}PdSP@rGO could be used as an efficient nanozyme for colorimetric ACP detection without resorting to destructive H₂O₂. A good linear relationship from 0.01 to 6.0 mU/mL with a detection limit of 8.3 μU/mL is obtained, which is better than most previously reported ACP assays. Importantly, the excellent assay performance could be successfully applied to ACP determination in serum samples with high accuracy. This study demonstrates that the enzyme-like activity of nanomaterials could be finely tuned simultaneously by controlling their exposed crystal facets and high specific surface area.

Detecting acid phosphatase enzymatic activity with phenol as a chemical exchange saturation transfer magnetic resonance imaging contrast agent (PhenolCEST MRI)

Phenol contains an exchangeable hydroxyl proton resonant at 4.8 ppm from the resonance frequency of water in the 1H nuclear magnetic resonance (1H NMR) spectrum, enabling itself to be detected at sub-mM concentration by either chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) or exchange-based T2 relaxation enhancement (T2ex) effect under acidic and basic conditions, respectively. We recently investigated the T2ex effects of phenol and its derivatives, but the CEST characteristics of phenols are unknown in detail, and no study on using the natural CEST MRI effects of phenol for detecting enzymatic activity has been conducted. Herein, on the basis of the inherent CEST MR property of phenol, namely phenolCEST, we developed the first MRI approach to detect acid phosphatase (AcP) enzymatic activity. Upon the activity of AcP at pH = 5.0, non-CEST-detectable enzyme substrate phenyl phosphate was converted to CEST-detectable phenol, providing a simple way to quantify AcP activity directly without the need for a second signalling probe. We showed the application of this phenolCEST biosensor for measuring AcP activity in both enzyme solutions and cell lysates of prostate cells. This work opens a door for the utilization of phenolCEST MRI technique in sensor design and development.

Determination of prostate cancer biomarker acid phosphatase at a copper phthalocyanine-modified screen printed gold transducer

In this work, a novel sensor based on immobilised copper phthalocyanine, 2,9,16,23-tetracarboxylic acid-polyacrylamide (Cu(II)TC Pc-PAA) was developed for determination of acid phosphatase (ACP) levels in nanomolar quantities. Detection was based on the measurement of enzymatically generated phosphate, with initial studies focused on phosphate detection at a Cu(II)TC Pc-PAA modified screen-printed gold transducer. The sensor was characterised in relation to operational performance (pH, response time, stability, linearity, and sensitivity) and common anionic interferents (nitrate, sulphate, chloride, and perchlorate). The functionalised surface also facilitated rapid detection of the enzyme bi-product 2-naphthol over the range 5-3000 μM. Quantitation of ACP was demonstrated, realising a linear response range of 0.5-20 nM and LOD of 0.5 nM, which is within the clinical range for this prostate cancer biomarker.

PdPt bimetallic nanowires with efficient oxidase mimic activity for the colorimetric detection of acid phosphatase in acidic media

PdPt bimetallic alloy nanowires (Pd/Pt NWs) were found to exhibit excellent oxidase-like activity and can be applied to sensitively detect the activity of acid phosphatase (ACP) in acidic media.

Achieving deep-red-to-near-infrared emissions in Sn-doped Cu-In-S/ZnS quantum dots for red-enhanced white LEDs and near-infrared LEDs

Semiconductor quantum dots (QDs) are promising luminescent materials for use in lighting, display and bio-imaging, and the color tuning is a necessity for such applications. In this work, we report tunable colors and deep-red or near infrared (NIR) emissions in Cu-In-S and Cu-In-S/ZnS QDs by incorporating Sn. These QDs (with a size of 5 nm) with varying Sn concentrations and/or Cu/In ratios were synthesized by a non-injection method, and characterized by a variety of analytical techniques (i.e., XRD, TEM, XPS, absorption, photoluminescence, decay time, etc.). The Cu-Sn-In-S and Cu-Sn-In-S/ZnS QDs with Cu/In = 1/2 show the emission maximum in the ranges of 701-894 nm and 628-785 nm, respectively. The red-shift in emission is ascribed to the decrease of the band gap with the Sn doping. The highest quantum yield of 75% is achieved in Cu-Sn-In-S/ZnS with 0.1 mmol Sn and Cu/In = 1/2. Both the white and NIR LEDs were fabricated by using Cu-Sn-In-S/ZnS QDs and a 365 nm LED chip. The white LED exhibits superhigh color rendering indices of Ra = 97.2 and R9 = 91 and a warm color temperature of 2700 K. And the NIR LED shows an interesting broadband near-infrared emission centered at 741 nm, allowing for applications in optical communication, sensing and medical devices.

Optical sensing at the nanobiointerface of metal ion-optically-active nanocrystals

Optically-active nanocrystals (such as quantum dots and plasmonic noble metal nanoparticles) have received great attention due to their size-tunable optical properties. The indicator displacement assay (IDA) with optically-active nanocrystals has become a common practice for optical sensor development, since no sophisticated surface functionalization of nanoparticles is required. Among the IDA-based optical sensors, the use of metal ions as receptors seems to be attractive. Therefore, in this review, the research progress of optical sensing at the nanobiointerface of metal ion-optically-active nanocrystals has been summarized. In particular, metal ion-mediated selective recognition has been summarized here based on the classical Hard-Soft-Acid-Base (HSAB) principle, which has been seldom mentioned before. Most of the references were therefore categorized according to their located place based on the HSAB theory. Besides, several metal ion modulation strategies that were not related to the HSAB theory (e.g., redox modulation) were also included. Finally, due to the cross-talk of metal ions in selective recognition, we have also summarized sensor array development based on multiple metal ion receptors in IDA sensing with optically-active nanocrystals. Several interesting applications of the IDA sensing with metal ions as receptors and optically-active nanocrystals as indicators are presented, with specific emphasis on the design principles and photophysical mechanisms of these probes.

Fluorescence imaging of hepatocellular carcinoma with a specific probe of COX-2

Hepatocellular carcinoma (HCC) is the major subtype of primary liver cancer. Although the standard treatment method based on surgery has generally extended life, it still causes the second and sixth most prevalent cancer-related death in men and women, respectively. The recurrence of cancer caused by unclear resection margins and any remaining undiscovered metastatic nodules should take a large proportion of responsibility for the poor prognosis after resective surgery. Therefore, a practical and effective method that can be used during hepatectomy to specifically identify HCC is a potentially significant area deserving attention. Tests involving fluorescence have been used in many biological systems. In this study, we use a probe that can combine with cyclooxygenase-2 (COX-2) and subsequently emit fluorescence to identify HCC cells and heteroplastic tumors in a mouse model. The results show that this specific probe can clearly differentiate HCC, with differences that could be observed with the naked eye in human samples. The biotechnology of knocking down COX-2 and its inhibitor were used on human HCC cell line SMMC7721, and the outcomes confirmed the above results. The toxic effect also showed that the probe had no harmful effect on normal liver cells. Taken together, our study demonstrates that a COX-2-specific fluorescence probe may be a new and effective method to identify HCC, especially during surgery.

A ‘turn-on’ fluorescent probe for lysosomal phosphatase: a comparative study for labeling of cancer cells

A turn-on fluorescent probe (LP1) discriminates cancer cells from normal cells based on expression of phosphatase in lysosomes.

Flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblast cancer cells using MWCNTs-Pdnano/PTCA/aptamer as labeled aptamer for the signal amplification

In this research, we demonstrated a flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblasts (CCRF-CEM) based on poly(3,4-ethylenedioxythiophene) decorated with gold nanoparticles (PEDOT-Au_nano) as a nano platform to immobilize thiolated sgc8c aptamer and multiwall carbon nanotubes decorated with palladium nanoparticles/3,4,9,10-perylene tetracarboxylic acid (MWCNTs-Pd_nano/PTCA) to fabricate catalytic labeled aptamer. In the proposed sensing strategy, the CCRF-CEM cancer cells were sandwiched between immobilized sgc8c aptamer on PEDOT-Au_nano modified surface electrode and catalytic labeled sgc8c aptamer (MWCNTs-Pd_nano/PTCA/aptamer). After that, the concentration of CCRF-CEM cancer cells was determined in presence of 0.1 mM hydrogen peroxide (H₂O₂) as an electroactive component. The attached MWCNTs-Pd_nano nanocomposites to CCRF-CEM cancer cells amplified the electrocatalytic reduction of H₂O₂ and improved the sensitivity of the sensor to CCRF-CEM cancer cells. The MWCNT-Pd_nano nanocomposite was characterized with transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to confirm the stepwise changes in the electrochemical surface properties of the electrode. The proposed sandwich-type electrochemical aptasensor exhibited an excellent analytical performance for the detection of CCRF-CEM cancer cells ranging from 1.0 × 10¹ to 5.0 × 10⁵ cells mL^-1. The limit of detection was 8 cells mL^-1. The proposed aptasensor showed high selectivity toward CCRF-CEM cancer cells. The proposed aptasensor was also applied to the determination of CCRF-CEM cancer cells in human serum samples.

Chitosan-stabilized platinum nanoparticles as effective oxidase mimics for colorimetric detection of acid phosphatase

Capping molecules on the surface of nanomaterials not only enhance the dispersion and stability of nanomaterials but also greatly facilitate their surface modification and biological applications. However, most capping molecules can severely block the active sites of the catalytic core, thereby decreasing the enzymatic activity of nanomaterial-based enzyme mimics. This work demonstrates the superiority of chitosan (Ch) as a capping molecule for synthesizing catalytic platinum nanoparticles (PtNPs). The experimental results show that Ch simultaneously exhibits an excellent stabilizing effect and enhances the oxidase-like activity of PtNPs. Kinetic studies indicate that Ch-PtNPs have a higher affinity for 3,3',5,5'-tetramethylbenzidine (TMB) than other kinds of oxidase mimics. Furthermore, the TMB chromogenic reaction catalyzed by Ch-PtNPs is found to be much faster in an acidic medium, thus adapting well to the optimal pH for acid phosphatase (ACP). Therefore, a novel colorimetric approach for ACP determination is developed for the first time, which is based on the Ch-PtNP-catalyzed oxidation of TMB, the inhibitory effect of ascorbic acid (AA) on the oxidase-like activity of Ch-PtNPs, and the ACP-catalyzed hydrolysis of AA 2-phosphate (AAP) into AA. The linear range for ACP is 0.25-2.5 U L^-1 and the limit of detection is measured to be 0.016 U L^-1. This new colorimetric method is utilized to detect ACP in real biological samples and to screen ACP inhibitors. We believe that these new PtNPs, which exhibit high colloidal stability, excellent catalytic performance, good biocompatibility, simple preparation, and easy modification, can be promising candidates for a broad range of applications in optical sensing, environmental monitoring, clinical diagnosis, and drug discovery.

Multi-stimuli responsive copper nanoclusters with bright red luminescence for quantifying acid phosphatase activity via redox-controlled luminescence switch

Thiolate-protected copper nanoclusers (CuNCs) are emerging as a promising class of luminescent materials since its unique optical properties such as aggregation-induced emission (AIE) and intriguing molecular-like behavior have been explored for sensing application. In this work, multi-stimuli responsive property of CuNCs was first investigated in depth and further adopted to develop a reliable and sensitive ACP assay. Penicilamine-capped CuNCs from a facile one-pot synthesis possess bright red luminescence and distinctive multi-stimuli responsive behaviors. Its sensitive and reversible response in luminescence to pH and temperature is originated from its inherent AIE property, and can be constructed as luminescent nanoswitches controlled by these external stimuli for precisely monitoring the change of environmental pH or temperature. The specific redox-responsive behavior of CuNC aggregates is found from severe luminescence quenching in the presence of a small amount of ferric or silver ions, and this sensitive response in luminescence to the preceding species is proved to be due to the conversion of Cu(II) from copper atoms with lower valence inside CuNCs. The luminescence switch of CuNC aggregates controlled by specific external potentials is further utilized to design a novel detection strategy for ACP activity. The great difference in luminescence quenching of CuNCs induced by iron(III) pyrophosphate (FePPi₂) complex and free ferric ions enables us to quantitatively monitor ACP level by the luminescence change as variation of ACP activity in the assay solution. This assay is able to detect ACP level as lower as 0.8 U/L, and covers a broad linear scope of 100.0 U/L. This work reports redox-responsive property of CuNCs and its underlying nature due to the oxidation of its interior copper atoms, and provides a sensitive assay method for ACP activity which is sufficiently sensitive for practical measurement in real 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.

Application of semiconductor quantum dots in bioimaging and biosensing

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing.

Highly sensitive detection of acid phosphatase by using a graphene quantum dots-based förster resonance energy transfer

A novel and effective fluorescence strategy was developed for sensitive and selective detection of acid phosphatase (ACP). A förster resonance energy transfer (FRET) biosensor was established by attaching nile red (NR) to graphene quantum dots (GQDs) via lecithin/β-Cyclodextrin (lecithin/β-CD) complex as the linker. The introduction of lecithin/β-CD would brought GQDs-NR pair close enough through both electrostatic interaction and hydrophobic interaction, thereby making the FRET occur and thus resulting in the fluorescence quenching of GQDs (donor) and meanwhile the fluorescence enhancement of NR (acceptor). The presence of ACP in the sensing system would catalyze the hydrolysis of lecithin into two parts, resulting in the GQDs-NR pair separation. Meanwhile, considerable fluorescence recovery of GQDs and decreasing of NR was observed due to the inhibition of FRET progress. In this method, the limit of detection (LOD) is 28µUmL^-1 which was considerably low for ACP detection. Using the GQDs-based fluorescence biosensor, we successfully performed in vitro imaging of human prostate cancer cells.

Sensitive detection of acid phosphatase based on graphene quantum dots nanoassembly

Mechanism for the detection of ACP based on the aggregation of GQDs.

Graphene quantum dots as selective fluorescence sensor for the detection of ascorbic acid and acid phosphatase via Cr(vi)/Cr(iii)-modulated redox reaction

A facile and rapid fluorescence assay based on a redox reaction for successively detecting ascorbic acid and acid phosphatase was developedviaCr(vi)-modulated graphene quantum dots (GQDs).

A novel ratiometric dual-emission fluorescence magnetic nanohybrid for HIgG immunoassay

The proposed ratiometric dual-emission (carbon dots and QDs) fluorescence magnetic nanohybrid displayed excellent analytical performance for the detection of HIgG.

Synthesis of functionalized fluorescent gold nanoclusters for acid phosphatase sensing

A novel and convenient one-pot but two-step synthesis of fluorescent gold nanoclusters, incorporating glutathione (GSH) and 11-mercaptoundecanoic acid (MUA) as the functionalized ligands (i.e. AuNCs@GSH/MUA), is demonstrated. Herein, the mixing of HAuCl4 and GSH in aqueous solution results in the immediate formation of non-fluorescent GSH-Au(+) complexes, and then a class of ∼2.6 nm GSH-coated AuNCs (AuNCs@GSH) with mild orange-yellow fluorescence after several days. Interestingly, the intense orange-red emitting ∼1.7 nm AuNCs@GSH/MUA can be synthesized within seconds by introducing an alkaline aqueous solution of MUA into the GSH-Au(+) complexes or AuNC@GSH solution. Subsequently, a reliable AuNC@GSH/MUA-based real-time assay of acid phosphatase (ACP) is established for the first time, inspired by the selective coordination of Fe(3+) with surface ligands of AuNCs, the higher binding affinity between the pyrophosphate ion (PPi) and Fe(3+), and the hydrolysis of PPi into orthophosphate by ACP. Our fluorescent chemosensor can also be applied to assay ACP in a real biological sample and, furthermore, to screen the inhibitor of ACP. This report paves a new avenue for synthesizing AuNCs based on either the bottom-up reduction or top-down etching method, establishing real-time fluorescence assays for ACP by means of PPi as the substrate, and further exploring the sensing applications of fluorescent AuNCs.