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Recent advances in the detection and removal of heavy metal ions using layered double hydroxide-based nanosensors and nanosorbents are summarized.

A chemical warfare agent sensor array based on organophosphorus-H2O2 reaction-regulated chemiluminescence is proposed.

A two-in-one cationic AIEgen micelle-boosted chemiluminescent H2O2 assay with improved sensitivity is presented.

Near-infrared persistent phosphors (NIR-PPs) are an emerging category of luminescent materials that can continuously emit NIR luminescence with super-long decay time of minutes, hours, or even days after the excitation ceases. Their unique excitation-free long-lasting afterglow, together with the NIR emission, has not only attracted wide research interests in the areas of photochemistry, photophysics, spectroscopy, and materials science, but also stimulated advanced applications in biosensing, bioimaging, biomedicine, and therapy in the past decade. Beyond these bio-related applications, the active research field triggers a number of novel applications recently. In this review, a brief outline of NIR-PPs including the luminescence mechanism, main material systems, and how they were applied into various fields was depicted. Particular emphasis was put on the emerging applications outside the field of biology. Future perspectives in this exploration research area were also presented. We hope this review can help researchers grab the latest information in the fast-growing field of NIR-PPs.

Gold nanoparticles with special surface plasmon resonance have been widely used in sensing and therapy because of their easy preparation, unique optical properties, excellent biocompatibility, etc. The applications of gold nanoparticles in chemo/biosensing, imaging, and therapy reported in 2016-2019, are summarized in this review. Regarding the gold nanoparticle-based sensing or imaging, sensing mechanisms and strategies are provided to illustrate the concepts for designing sensitive and selective detection platforms. Gold nanoparticlemediated therapy is introduced by surface plasmon resonance-based therapy and delivery-based therapy. Beyond the sole therapeutic system, platforms through synergistic therapy are also discussed. In the end, discussion of the challenges and future trends of gold nanoparticle-based sensing and therapy systems is described.

Gold nanorods (GNRs) with desired longitudinal localized surface plasmon resonance (LLSPR) and strong scattering intensity are important for extending their practical applications in bioimaging and sensing. Herein, a simple additive (HCl and Na2S)-regulated overgrowth approach has been proposed for preparing GNRs with tunable LLSPR. In this approach, HCl is used to slow down the growth reaction rate by changing chemical equilibrium, while Na2S is utilized to halt the reaction when LLSPR is reaching the expected wavelength under monitoring by a UV-Vis spectrometer. Under optimal conditions, GNRs with an LLSPR range from 850 to 650 nm could be facilely prepared with a high precision of 3 nm deviation. The TEM images reveal that GNRs have high monodispersity, displaying an increase in both length and diameter but a decrease in the aspect ratio. With the increase in size, the produced GNRs show enhanced scattering intensity and are applicable for single nanoparticle imaging due to the enlarged absorption and scattering cross-section and improved matching efficiency toward the CCD response.

The sensitive and selective perception of dopamine (DA, a typical neurotransmitter) is important to evaluate the biological environment. In this study, a catechin-functionalized gold nanocluster (C-Au NC) nanoprobe has been explored for the ratiometric DA sensing. The detection mechanism is based on the formation of azamonardine via selective DA-catechin chemical reaction and subsequent enhanced fluorescence emission. Using Au NC emission as the internal reference, ratiometric fluorescence variation is realized, which allows sensitive DA analysis with a limit of detection of 1.0 nM (S/N = 3) and linear response concentration range from 0 to 500 nM. The characteristic chemical reaction between catechin and DA affords favorable selectivity over other amino acids, metal ions and small molecules. In addition, the practical application of the proposed nanoprobe is validated by the accurate detection of DA content in urea and cell lysate samples.

The development of simple Fenton/Fenton-like systems with durative hydroxyl radical (•OH) generation characteristics is significant to rapid organic pollutant degradation and cost-effective water treatment. In this study, a tris(hydroxymethyl)aminomethane (Tris)-incorporated Co(II)-H2O2 Fenton-like system has been successfully constructed for efficient Sunset Yellow (SY, a typical anionic azo dye) degradation under alkaline conditions. The mechanism of the enhanced degradation consists of two parts: first, the Tris-Co(II) complex triggers the durative generation of highly oxidized hydroxyl radicals; second, electrostatic attraction between SY and the Tris-Co(II) complex shortens the radical-SY interaction time and facilitates the degradation of SY. With the introduction of Tris to this proposed system, the decolorization rate of SY can be increased from 37.0 to 98.0% after 50 min and efficient SY degradation with a high total organic carbon removal efficiency (>59.0%) is achieved under a wide initial pH from 8.7 to 12.0. Moreover, the universality of the designed system for anionic azo dye degradation is verified with reactive red and congo red.

Gold nanoclusters (Au NCs) with atomic precision have huge application potentials in chemo/bio sensing, catalysis, and energy conversion. However, a precise atomic control of Au NCs still remains a great challenge. Herein, we developed a facile one-pot and top-down strategy to synthesize eight-atom numbered Au NCs (Au8 NCs), aiming to understand their fundamental physicochemical properties and explore their potential applications. The etching of gold nanoparticles by their encapsulated hyperbranched polyethyleneimine was significantly promoted by a newly proposed catalyst, hydrogen peroxide, which gave rise to brightly blue-emitting Au8 NCs (quantum yield = 28.8%). The as-prepared Au8 NCs could sense hemoglobin with a detection limit of 5.0 nM through the combination of Fenton reaction and fluorescence resonance energy transfer. And the sensing behaviour is unaffected by the presence of various interferents such as proteins, small molecules, anions, and metal ions. In addition, a hemoglobin evaluation in blood samples with small relative standard deviations and satisfied recoveries was achieved using the proposed Au8 NC nanoprobes.

The rapid and effective recognition techniques for crystal facets in noble metal nanocrystals (NCs) are highly desirable in evaluation of their catalytic performances. Herein, it was found that the variation trend of cataluminescence (CTL) intensity in the presence of propanol was proportional to the crystal facets index change of LDH-supported Pd@Au NCs. The mechanism investigation for the propanol-triggered CTL on the surface of layered double hydroxide (LDH)-supported Pd@Au NCs revealed that the abundant negative charge in the high-index facets of LDH-supported Pd@Au NCs facilitated electron transfer between NCs and volatile propanol, resulting in acceleration of the CTL reactions. Accordingly, the propanol-triggered CTL can be as an indicator for rapid screening of crystal facets in NCs. Its universality had further been verified by screening crystal facets in LDH-supported Pd NCs. The crystal facets detected by propanol CTL probe were well-matched with those obtained by conventional high-resolution transmission electron microscope. The proposed CTL strategy exhibits some advantages, such as convenient operation, rapid response, long-term stability, and low cost. And it is expected crystal facets of other kinds of NCs could be screened by replaceable CTL probe.

Luminol tablet-Tris-Co(ii) complex-PVP-H2O2 systems exhibit 13 hours of intensive and stable chemiluminescence (CL) due to the continuous generation of ˙OH and sustained-release. Multicolored chemical lights were prepared through CL resonance energy transfer. This work presents a new method for the fabrication of bright chemical lights in aqueous solution for emergencies.

Carminic acid (CA) extracted from cochineal is widely used in food additives as a natural colorant, and its potential risk to human health makes its detection important. In this work, a layered doubled hydroxide (LDH)–luminol–H2O2 system-based chemiluminescence (CL) platform has been successfully applied for CA sensing. The principle detection consists of two steps: first, LDH adsorbs CA onto the surface via electrostatic attraction; second, CA quenches the CL of the LDH–luminol–H2O2 system via the synergistic effect of CL resonance energy transfer, reduction of reactive oxygen species, and occupation of positively charged centers of brucite-like layers. With this CL approach, 0.5 μM CA is detectable using a CL spectrometer, and the limit of detection is 0.03 μM. This CL system exhibited a linear response to CA in the concentration range from 0.5 to 10 μM. In addition, the practical application of the designed CL sensing system is evaluated with dried pork slice samples.

Monoaromatic molecules are a category of molecules containing a single aromatic ring which generally emit light in the ultraviolet (UV) region. Despite their facile preparation, the UV emission greatly limits their application as organic probes. In this study, we developed a general method to red shift the emission of monoaromatic molecules. Significant fluorescence red-shift (∼100 nm per intramolecular hydrogen bonding) can be achieved by introducing intramolecular hydrogen bonding units to benzene, a typical monoaromatic molecule. Upon increasing the number of hydrogen bonding units on the benzene ring, UV, blue, and green emissions are screened, which are switchable by simply breaking/restoration the intramolecular hydrogen bonding. As a demonstration, with the breaking of one intramolecular H-bonding, the green emission (λemmax = 533 nm) of 2,5-dihydroxyterephthalic acid (DHTA) changed to cyan (λemmax = 463 nm) upon the formation of its phosphorylated form (denoted as PDHTA), which, in the presence of alkaline phosphatase (ALP), hydrolyzed and recovered the green emission. By taking advantage of the switchable emission colors, ratiometric in vitro and endogenous ALP sensing was achieved. This general approach offers a great promise to develop organic probes with tunable emissions for fluorescence analysis and imaging by different intramolecular hydrogen bonding.

Plasmonic nanoparticles with special localized surface plasmon resonance (LSPR) characters have been widely applied for optical sensing of various targets. With the combination of single nanoparticle imaging techniques, dynamic information of reactions and biological processes is obtained, facilitating the deep understanding of their principle and design of outstanding nanomaterials. In this review, we summarize the recently adopted optical analysis of diverse analytes based on plasmonic nanoparticles both in homogeneous solution and at the single-nanoparticle level. A brief introduction of LSPR is first discussed. Colorimetric and fluorimetric homogeneous detection examples by using different sensing mechanisms and strategies are provided. Single plasmonic nanoparticle-based analysis is concluded in two aspects: visualization of chemical reactions and understanding of biological processes. The basic sensing mechanisms and performances of these systems are introduced. Finally, this review highlights the challenges and future trend of plasmonic nanoparticle-based optical analysis systems.

Improper use of food additives may lead to potential threat to human health, making it important to develop sensitive and selective method for their detection. Nanomaterials with unique chemical and electrochemical properties show extensive applications in the design of food additive sensing systems. In this review, we summarize the recently adopted electrochemical and optical analysis of food additives based on nanomaterials. Detection of typical food additives (colorants and preservatives) by using different sensing mechanisms and strategies are provided. In addition, determination of illegal food additives is also briefly introduced. Finally, this review highlights the challenges and future trend of nanomaterial-based food analysis system.

The detection of cyanide anion (CN−), a highly toxic pollutant, has attracted growing attention in the past years. In this work, a nanosensor composed of hyperbranched polyethyleneimine (hPEI)-assisted dual-emissive gold nanoclusters (DE-Au NCs) is proposed for ratiometric detection of CN− based on surface valence state-driving etch. The ratiometric color change of fluorescence is based on a fact that the red-emissive Au NCs with a high content of surface Au(I) can be easily etched by CN−, while the blue-emissive Au NCs with nearly neutral character can resist CN−. Because of the specific gold-CN− chemistry and electrostatic attraction between the positively charged hPEI protecting layer and the negatively charged CN−, the DE-Au NC-based nanosensor provides high selectivity toward CN− over other anions with a limit of detection of 10 nM. Practical application of the proposed DE-Au NC nanosensor is verified by satisfying recoveries of CN− determination in river water and urine samples.

Gold nanorods (GNRs) with desired longitudinal localized surface plasmon resonance (LLSPR) and strong scattering intensity are important for extending their practical applications in bioimaging and sensing. Herein, a simple additive (HCl and Na

Developing probes for sensitive H 2 O 2 detection is critical for understanding its related physiological and pathological processes. In this study, novel carbon quantum dot-gold nanocluster (CQD-AuNC) nanosatellite with high fluorescence energy transfer efficiency (∼40%) and dual-emission fluorescent properties have been exploited for fluorescence ratiometric sensing of H 2 O 2 . The sensing mechanism was based on the fact that H 2 O 2 can quench the red emission of AuNCs. Under the optimal conditions, the CQD-AuNC nanosatellite probe was sensitive to H 2 O 2 in the range from 5.0 nM to 80 nM with a limit of detection of 2.9 nM. The practicality of the proposed CQD-AuNC nanosatellite probe was validated by imaging H 2 O 2 in living cells.

In this report, a simple approach for generating chemiluminescence (CL) of hyperbranched polyethyleneimine protected silver nanoclusters (hPEI-AgNCs) in solution by hydroxyl radicals (˙OH) is proposed. Emission of this CL system originates from excited AgNCs rather than from reaction intermediates, which is different from other metal nanoclusters involving CL reactions. Notably, in the presence of tea polyphenols (TPPs), the ˙OH induced CL signal is restrained, which is due to the TPPs-induced reduction of ˙OH. Therefore, a facile CL approach for TPPs sensing based on the inhibition effect of TPPs towards the ˙OH has been developed. This simple CL detection method exhibits a linear response toward TPPs in the concentration range from 2.52 to 76.2 μM with a limit of detection of 2.52 μM. In addition, the proposed method displays high selectivity toward TPPs over other small molecules or metal ions, including L-theanine, L-alainine, L-asparagine, paraxanthine, glycine, glucose, Na+, K+, Mg2+, Zn2+ and Fe3+. Compared with reported colorimetric or fluorimetric approaches, this new system shows comparable or better selectivity. The proposed method can be readily used for TPPs content evaluation from tea sample infusions.

In this report, a simple chemiluminescence (CL) approach for detecting an anionic dye, alizarin red S (ARS), based on layered double hydroxides (LDHs)-improved CL from hydrogen peroxide (H2O2) and luminol system is proposed. The LDHs-improved H2O2–luminol CL is due to the adsorption of luminol dianion and peroxide anion onto the positively charged brucite-like layers and the facilitated formation of carbonate radicals, which benefits the generation of light-emitting intermediate 3-aminophthalate anions. Notably, the LDHs-improved H2O2–luminol CL signal is markedly restrained in the presence of ARS, which is assigned to the ARS-mediated occupation of the positively charged centres on the brucite-like layers and the inhibition of the formation of 3-aminophthalate anions. Thus, a facile CL method for ARS perception based on the suppression effect of ARS toward the LDHs-improved H2O2–luminol CL has been developed. This simple CL approach shows a limit of detection of 0.1 μM toward ARS and exhibits a linear response in the concentration range from 0.5 to 30 μM. In addition, the proposed method exhibits a high specificity toward ARS over other small molecules, metal ions or anions. Furthermore, the practical application of the proposed method for ARS sensing is evaluated with the dye wastewater samples.

Plasmonic nanoparticle-based colorimetric sensing has gained wide attention due to its advantages including rapidity, simplicity and expensive instrument-free characters. In the present study, Ag–Au bimetallic nanoparticles were proposed as novel optical probes to determine cobalt ion (Co2+) concentration. The sensing mechanism is based on the fact that Co2+ can react with ethylenediamine (en) and S2O32− to form (en)2CoS2O3+ on the nanoparticle surface, which can decrease the negative charge of the nanoparticle, reduce the repulsion between adjacent nanoparticles, and subsequently induce nanoparticle aggregation, was verified by dynamic light scattering. The effects of several parameters on the detection sensitivity, including the concentration of S2O32− and en, pH value and incubation time, were investigated. The assay demonstrated high selectivity toward Co2+ in the presence of K+, Cu2+, Pb2+, Ag+, Zn2+, Ba2+, Mn2+, Fe2+, Fe3+, Ni2+ and Hg2+. Under optimal conditions, the absorbance ratio of A600/A434 showed a linear relationship versus Co2+ concentration from 0 to 0.6 μM with a correlation coefficient (R2) of 0.980, and the detection limit was calculated to be 0.02 μM. The practical application of the proposed nanoprobes was evaluated with river and tap water samples.

Cataluminescence (CTL) is a specific chemiluminescence (CL) occurring on the surface of solid catalysts during heterogeneous catalytic oxidation reactions, and it is still a young technique compared to conventional CL. In recent years, CTL-based sensors have been widely used in the detection of various analytes. We have witnessed many developments in CTL-based sensing systems for the enhancement of sensitivity or selectivity. This review provides a thorough introduction to the history and development of CTL-based sensing systems. We have briefly discussed the working principles for CTL systems and related the influencing factors first. The development of CTL based on these factors and instruments has been subsequently introduced. Several excellent CTL-based sensing systems have been discussed to highlight their practicality for the analysis of complicated environmental samples. Discussions of the challenges and future trends of CTL-based sensing systems have been provided in the end of this review.

In present study, we discovered unusual solvent-mediated aggregation-enhanced emission (AEE) character of 11-mercaptoundecanoic acid capped gold nanoclusters (MUA-Au NCs). When aggregated in aqueous media, the MUA-Au NCs showed strong emission, which was weakened by adding ethanol. Interestingly, the suppressed emission was selectively enhanced in the presence of hydrogen sulfide (H2S) because H2S was absorbed onto Au NCs through the strong sulfur-gold bonding affinity. The hydrolyzed H2S, namely, HS−, made the Au NCs negatively charged, which aggregated again due to decreased solubility. The H2S-mediated fluorescence enhancement can be further amplified by introducing a hydrophilic thiolate (glutathione, GSH) onto the surface of Au NCs (GSH/MUA-Au NCs), which enabled sensitive determination of H2S. Under the optimized condition, a detection limit of 35 nM was achieved. The determination was not interfered by other anions such as F−, Cl−, Br−, I−, OAc−, N3−, NO3−, HCO3−, SCN−, SO32−, and SO42−. This excellent sensing performance allowed practical application of the GSH/MUA-Au NC-based sensing platform to accurate determination of H2S in human serum samples.

The development of simple Fenton/Fenton-like systems with durative hydroxyl radical (•OH) generation characteristics is significant to rapid organic pollutant degradation and cost-effective water treatment. In this study, a tris(hydroxymethyl)aminomethane (Tris)-incorporated Co(II)–H2O2 Fenton-like system has been successfully constructed for efficient Sunset Yellow (SY, a typical anionic azo dye) degradation under alkaline conditions. The mechanism of the enhanced degradation consists of two parts: first, the Tris–Co(II) complex triggers the durative generation of highly oxidized hydroxyl radicals; second, electrostatic attraction between SY and the Tris–Co(II) complex shortens the radical–SY interaction time and facilitates the degradation of SY. With the introduction of Tris to this proposed system, the decolorization rate of SY can be increased from 37.0 to 98.0% after 50 min and efficient SY degradation with a high total organic carbon removal efficiency (>59.0%) is achieved under a wide initial pH from 8.7 to 12.0. Moreover, the universality of the designed system for anionic azo dye degradation is verified with reactive red and congo red.

The rapid and sensitive visualization of 2,6-dipicolinic acid (DPA, a unique anthrax biomarker) is essential to prevent anthrax disease or biological terrorist attack. In this study, a Eu

The effective discrimination of dopamine (DA) analogues is an enduring challenge because of their very tiny structural differences, and thus a separation technique is generally required during the conventional analysis. In this study, a hyperbranched polyethyleneimine (hPEI)-based fluorescent sensor array has been constructed for the separation-free and effective differentiation of four DA analogues. The discrimination includes two steps: firstly, the formation of fluorescent polymer nanoparticles (FPNs) with diverse emission profiles via hPEI-mediated self-polymerization reaction of DA analogues and secondly, the linear discriminant analysis of fluorescence patterns of the formed FPNs for the differentiation of DA analogues. The hPEI-assisted self-polymerization reaction of DA analogues and substitution group mediated optical properties of the resulted FPNs enable an excellent discrimination of four DA analogues at a concentration of 1.0 μM when linear discriminant analysis and hierarchical cluster analysis are smartly combined. Additionally, binary, tertiary and even quaternary mixtures of analogues can also be well distinguished with the proposed sensor array. The practicability of this established sensor array is validated by a high accuracy (100%) evaluation of 88 blind samples containing a single analogue or a mixture of two, three or four analogues.

The exploitation of highly soluble and responsive AIEgens is essential for further expansion of their practical applications. In this study, dipropyltrimethylammonium bromide-substituted TPE (denoted as o-TPEDTA), a homolateral and dicationic AIEgen, was synthesized and applied for the turn-on detection of casein via hydrophobic interactions. The rapid and sensitive detection of casein was achieved using the designed o-TPEDTA probe with the limit of detection of 0.05 μg mL-1. The satisfying selectivity of over 1000-fold concentration of other probably existing chemicals, including amino acids, sugars and salts, was achieved due to the strong binding affinity between o-TPEDTA and casein. The evaluation of casein in milk powder samples with small relative standard deviations was realized using the o-TPEDTA probe. The accuracy of the o-TPEDTA probe-based detection method was validated by the consistency of the casein detection results with those obtained via a national standard casein evaluation approach.

Luminol tablet-Tris-Co(ii) complex-PVP-H2O2 systems exhibit 13 hours of intensive and stable chemiluminescence (CL) due to the continuous generation of ˙OH and sustained-release. Multicolored chemical lights were prepared through CL resonance energy transfer. This work presents a new method for the fabrication of bright chemical lights in aqueous solution for emergencies.

Protection/deprotection of thiolates are widely used for the design of sensing systems by producing free sulfydryl (–SH) groups. However, most conventional protection/deprotection strategies reported so far suffer poor protection and/or difficult release of –SH group. In this study, phosphorylation/dephosphorylation strategy that exhibits efficient protection and facile liberation of –SH group via the formation of a phosphate-thiol ester, was utilized to develop colorimetric probe for alkaline phosphatase (ALP) activity evaluation. The proposed probe was composed of a cysteamine S-phosphate as a model thiolate substrate and Zonyl FSN-100 functionalized gold nanoparticles (FSN-AuNPs) as reporters. In the presence of ALP, the cysteamine S-phosphate hydrolyzed to generate cysteamine, which aggregated FSN-AuNPs with detectable spectroscopic changes through nanointerface interactions. The changes in UV–vis absorption spectroscopy allowed a detection limit of ALP at 0.1 unit/L. The specific enzyme catalytic hydrolysis provided high selectivity toward ALP over other proteins, small molecules, and metal ions. The practicability of the sensor was validated by accurate examination of ALP in blood samples. In addition, by integrating the conventional ELISA technique and the proposed phosphorylation tactic, sensitive immunoglobulin G detection was achieved.

Development of selective cataluminescence (CTL) sensors toward volatile organic compounds (VOCs) is of great importance to environmental analysis and daily chemicals safety. Although some reports for the determination of VOCs based on CTL have been reported, part of them suffered relatively low selectivity because of their high sensitivity toward interferents. In this study, mesoporous TiO2 nanoparticles have been exploited to detect diethyl ether with the usage of a 440 nm bandpass filter. The proposed method showed high selectivity toward diethyl ether over other VOCs, such as acetaldehyde, acetone, butanone and butanol, etc. Such a high selectivity was majorly attributed to the difference of CTL emission profiles of various VOCs reaction intermediates, and only diethyl ether exhibited strong CTL emission at about 440 nm. Under the optimal conditions, diethyl ether could be detected ranging from 2.0 to 50.0 mM. Furthermore, the practical application of this proposed CTL sensor for diethyl ether was validated with artificial samples and commercial perfumes. In general, such a simple method with high selective detection through controlling detection range could be extended to other analytes.

Layered nanomaterial has become a popular hierarchical material for amplifying chemiluminescence (CL) in recent years, mainly because of its ease of preparation and modification, large specific surface area, and high catalytic activity. In this review, we mainly discuss layered-nanomaterial-amplified CL systems based on graphene and its derivatives, layered double hydroxides, and clay. Detection mechanisms and strategies of layered-nanomaterial-amplified CL systems are provided to show the basic concepts for designing sensitive and selective sensing systems. Strategies for expanding the applications of layered-nanomaterial-amplified CL systems by combination with surfactants, quantum dots, organic dyes, and nanoparticles are introduced for the analysis of various analytes in real samples. The challenges and future trends of layered-nanomaterial-amplified CL systems are discussed at the end of the review. Graphical Abstract Schematic illustration of layered nanomaterial amplified chemiluminescence.

As a highly carcinogenic pollutant but also an important food preservative, nitrite has attracted growing attention in the past few years. In this work, a hyperbranched polyethyleneimine protected silver nanocluster (hPEI-Ag NC) based nanosensor is proposed for the detection of nitrite. The sensing principle consists of two steps: nitrite reacts with hydrogen peroxide (H2O2) to generate peroxynitrous acid under acidic conditions, and the as-formed peroxynitrous acid then induces the aggregation and fluorescence quenching of hPEI-Ag NCs. Due to the specific nitrite–H2O2 chemistry, the hPEI-Ag NC based nanosensor shows high selectivity toward nitrite over other anions with a limit of detection of 100 nM. The practical application of the proposed nanosensor has been validated with lake water, tap water and seawater samples.

In this study, we employed ultrasound-based treatment to mediate the emission properties of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide-capped gold nanodots (11-MUTAB-Au NDs). The as-prepared 11-MUTAB-Au NDs (sizes: ca. 1.8 nm), obtained from the reaction of gold nanoparticles (ca. 3 nm) and 11-MUTAB, exhibited very weak red photoluminescence (PL) near 670 nm [quantum yield (QY): 0.01%] upon excitation at 365 nm. After ultrasonication (20 W) for 2 h, however, the 11-MUTAB-Au NDs exhibited a >1000-fold enhancement in their PL intensity (QY: 11.5%), which shifted to a green color (ca. 540 nm) with a longer PL lifetime, due to the smaller size of the resulting NDs and the higher density of their capping 11-MUTAB ligands. Moreover, the PL of the 11-MUTAB-Au NDs returned to the near-infrared region (ca. 810 nm) after ultrasonication for a long period of time (>5 h). The dramatically different optical properties of these alkanethiol-protected Au NDs after ultrasonication were presumably due to variation in their ligand densities; these effects were highly regulated by varying the ultrasonication time and power. Because the size, oxidation state, surface ligand density, and PL of these Au NDs could be controlled simply through ultrasonic treatment, this approach might open up new avenues for the preparation of emission-tunable metallic (e.g., Au, Ag, Pt) NDs presenting various capping ligands.

The rapid and sensitive visualization of 2,6-dipicolinic acid (DPA, a unique anthrax biomarker) is essential to prevent anthrax disease or biological terrorist attack. In this study, a Eu3+-labeled ethylenediaminetetraacetic acid loaded hyperbranched polyethyleneimine carbon nanodot (hPEI-CD-EDTA-Eu3+) nanoprobe has been proposed for the ratiometric DPA detection. The sensing mechanism is based on the rapid DPA-Eu3+ chelation within 30 s and subsequent enhanced fluorescence emission through the antenna effect. With the introduction of EDTA chelating unit, the resulted fluorescence of Eu3+-complex is greatly enhanced, which endows sensitive DPA perception. By employing hPEI-CD as the internal reference, ratiometric DPA sensing is realized with a good linearity in the concentration range from 1.0 to 100 nM, with a limit of detection of 190 pM (S/N = 3). The specific chelation affinity between Eu3+ and DPA provides satisfying selectivity over other amino acids and ions. Using nanoprobe-loaded polyvinylidene fluoride paper as the analytical device, point-of-care DPA visualization is achieved. Furthermore, the practical application of designed paper device is validated by the visual detection of metabolic DPA-release from Bacillus subtilis spores.

The electrochemiluminescence (ECL)-based simultaneous detection of multiple biomarkers in one sample has received considerable attention in the past decade due to the increasing need for accurate cancer diagnosis and prediction. However, there has not been a comprehensive summary of ECL-based simultaneous detection of multiple biomarkers. In this review, we focus on recent advances in multiplex ECL assays using diverse detection strategies and their applications for various biomarkers. Based on analyte-induced changes in ECL signals, systems for the simultaneous quantitation of biomarkers (e.g., microRNAs, proteins, and cancer cells) have been proposed. These systems are classified into the following four categories: spatial-resolved, potential-resolved, spectrum-resolved, and miscellaneous strategies. Finally, future perspectives for multiplex ECL-based simultaneous detection systems are discussed.

We proposed a π-conjugation enhanced molar absorption coefficient strategy that can effectively improve the sensitivity of the spectrophotometry sensing technique. As a case study, the strategy was demonstrated for sensitive nitrite detection based on the typical nitrite-thiol reaction.