Room temperature preparation of water-soluble polydopamine-polyethyleneimine copolymer dots for selective detection of copper ions

Integration of a biocompatible metal-phenolic network and fluorescence microspheres as labels for sensitive and stable detection of carbendazim with a lateral flow immunoassay

High fluorescence intensity microspheres such as aggregation-induced emission fluorescence microspheres (AIEFM) have improved the sensitivity of lateral flow immunoassay (LFIA). The preparation of immune probes in LFIA usually adopts the chemical coupling strategy with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide for antibody coupling, which has the problems of low coupling efficiency, tedious coupling process, and poor repeatability. A biocompatible metal-phenolic network (MPN), which contains large amounts of phenols and galloyl groups, could easily, quickly, and stably couple with antibodies. Herein, we proposed a strategy based on MPN modification on ultrabright AIEFM surface as a novel label for the rapid detection of carbendazim. The limit of detection of AIEFM@MPN-LFIA was 0.019 ng/mL, which was 4.9 times lower than that of AIEFM-LFIA. In spiked samples, the average recoveries of AIEFM@MPN-LFIA ranged from 80% to 118% (coefficient of variation <13.45%). Therefore, AIEFM@MPN was a promising signal label that could improve the detection performance of LFIA.

Immobilization of aldo-keto reductase on dopamine/polyethyleneimine functionalized magnetic cellulose nanocrystals to enhance the detoxification of patulin in fresh pear juice

Patulin (PAT) is a highly toxic mycotoxin, which can contaminate fruits and their products and cause harm to human health. Cellulose nanocrystals (CNCs) were functionalized by magnetite nanoparticles, dopamine (DA) and polyethyleneimine (PEI) to form a multifunctional nanocarrier (DA/PEI@Fe3O4/CNCs) for immobilizing aldo-keto reductase (MgAKR) to degrade PAT. The MgAKR-DA/PEI@Fe3O4/CNCs were reusable and environmentally friendly due to its surface area, high magnetization value, and oxygen/amine function. The immobilization method significantly improved reusability, resistance to proteolysis, temperature stability and storage stability of MgAKR-DA/PEI@Fe3O4/CNCs. With NADPH as a coenzyme, the detoxification rate of MgAKR-DA/PEI@Fe3O4/CNCs on PAT reached 100 % in phosphate buffer and 98 % in fresh pear juice. The quality of fresh pear juice was unaffected by MgAKR-DA/PEI@Fe3O4/CNCs and could be quickly separated by magnet after detoxification, which was convenient for recycling. It has broad application prospects in the control of PAT contamination in beverage products containing fruit and vegetable ingredients.

Nanotechnology-based analytical techniques for the detection of contaminants in aquatic products

Food safety of aquatic products has attracted considerable attention worldwide. Although a series of conventional bioassays and instrumental methods have been developed for the detection of pathogenic bacteria, heavy metal residues, marine toxins, and biogenic amines during the production and storage of fish, shrimp, crabs et al., the nanotechnology-based analyses still have their advantages and are promising since they are cost-efficient, highly sensitive and selective, easy to conduct, facial design, often require no sophisticated instruments but with excellent detection performance. This review aims to summarize the advances of various biosensing strategies for bacteria, metal ions, and small molecule contaminants in aquatic products during the last five years, The review highlights the development in nanotechnologies applied for biorecognition process, signal transduction and amplification methods in each novel approach, the nuclease-mediated DNA amplification, nanomaterials (noble metal nanoparticle, metal-organic frameworks, carbon dots), lateral flow-based biosensor, surface-enhanced Raman scattering, microfluidic chip, and molecular imprinting technologies were especially emphasized. Moreover, this study provides a view of current accomplishments, challenges, and future development directions of nanotechnology in aquatic product safety evaluation.

Bifunctional Cu(II)-containing PDA-PEI copolymer dots: Demonstration of a dual-mode platform for colorimetric-fluorescent detection of glyphosate in the environment

The reliable and accurate detection of glyphosate is urgently demanded because it is related to food and environmental safety. In this contribution, a PDA-PEI/Cu2+ complex that possesses peroxidase-mimetic activity and stimulus-responsive fluorescence was fabricated by coordinating Cu2+ with polydopamine-polyethyleneimine copolymer dots (PDA-PEI CPDs). With the introduction of Cu2+, the fluorescence intensity of PDA-PEI CPDs dropped sharply owing to the electron transfer effect. As a peroxidase-mimicking nanozyme, the PDA-PEI/Cu2+ complex owns catalytic capacity to oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB, leading a further fluorescence quenching by internal filtering effect by oxTMB. Once the glyphosate participated, the fluorescence signal of PDA-PEI CPDs is recovered significantly because of the formation of more stable Glyp-Cu2+ complexes, meanwhile the peroxidase-mimicking activity of PDA-PEI/Cu2+ complex could be strongly hindered. According to this principle, a novel and extremely convenient 'turn off' colorimetric and 'turn on' fluorescence sensing platform can be established for dual-mode detection of glyphosate. The favorable sensitivity and selectivity and were verified in the analysis of glyphosate in the environment through the marriage of dual-signal sensing platform. The detection limit of the dual-mode glyphosate sensing platform was 103.82 ng/mL for colorimetric assay and 16.87 ng/mL for fluorescent assay, respectively. Satisfactory recoveries in the range of 96.40%-104.66% were obtained, indicating the potential of this method for application in complicated real sample. Thereby, this strategy broadens the applications of polydopamine nanomaterials and holds a promising application in determination of pesticide residues.

Highly Selective Fluorescent Sensors: Polyethylenimine Derivatives of Triphenylamine and Coumarin for GTP and ATP Interaction via Fluorescence Lifetime Imaging Microscopy

Chemical derivatives of polyethylenimine (PEI) receptors with either triphenylamine (TPA) or 7-hydroxy-4-methyl-coumarin (Cou) form stable complexes with adenine and guanine nucleotides in water. The host-guest complex modulation is found to be based on noncovalent molecular interactions such as π-π stacking and hydrogen bonding, which are dependent on the aromatic moieties attached to the polyaminic (PEI) backbone. PEI-TPA acts as a chemosensor with a recognition driving force based on aggregation-induced emission (AIE), involving π-π interaction between the nucleic base and TPA. It detects GTP by a chelation enhancement quenching effect of fluorescence (CHEQ) with a measured logarithm stability constant, log β = 7.7. By varying the chemical characteristics of the fluorophore, as in the PEI-Cou system, the driving force for recognition changes from a π-π interaction to an electrostatic interaction. The coumarin derivative detects ATP with a log β value one order of magnitude higher than that for GTP, allowing for the selective recognition of the two nucleotides in a 100% aqueous solution. Furthermore, fluorescence lifetime imaging microscopy (FLIM) allows for a correlation between the selectivity of PEI-TPA toward nucleotides and the morphology of the structures formed upon ATP and GTP recognition. This study offers valuable insights into the design of receptors for the selective recognition of nucleotides in water.

Functionalization of and through Melanin: Strategies and Bio-Applications

A unique feature of nanoparticles for bio-application is the ease of achieving multi-functionality through covalent and non-covalent functionalization. In this way, multiple therapeutic actions, including chemical, photothermal and photodynamic activity, can be combined with different bio-imaging modalities, such as magnetic resonance, photoacoustic, and fluorescence imaging, in a theragnostic approach. In this context, melanin-related nanomaterials possess unique features since they are intrinsically biocompatible and, due to their optical and electronic properties, are themselves very efficient photothermal agents, efficient antioxidants, and photoacoustic contrast agents. Moreover, these materials present a unique versatility of functionalization, which makes them ideal for the design of multifunctional platforms for nanomedicine integrating new functions such as drug delivery and controlled release, gene therapy, or contrast ability in magnetic resonance and fluorescence imaging. In this review, the most relevant and recent examples of melanin-based multi-functionalized nanosystems are discussed, highlighting the different methods of functionalization and, in particular, distinguishing pre-functionalization and post-functionalization. In the meantime, the properties of melanin coatings employable for the functionalization of a variety of material substrates are also briefly introduced, especially in order to explain the origin of the versatility of melanin functionalization. In the final part, the most relevant critical issues related to melanin functionalization that may arise during the design of multifunctional melanin-like nanoplatforms for nanomedicine and bio-application are listed and discussed.

Folic Acid Adjustive Polydopamine Organic Nanoparticles Based Fluorescent Probe for the Selective Detection of Mercury Ions

Polydopamine fluorescent organic nanomaterials present unique physicochemical and biological properties, which have great potential application in bio-imaging and chemical sensors. Here, folic acid (FA) adjustive polydopamine (PDA) fluorescent organic nanoparticles (FA-PDA FONs) were prepared by a facile one-pot self-polymerization strategy using dopamine (DA) and FA as precursors under mild conditions. The as-prepared FA-PDA FONs had an average size of 1.9 ± 0.3 nm in diameter with great aqueous dispersibility, and the FA-PDA FONs solution exhibit intense blue fluorescence under 365 nm UV lamp, and the quantum yield is ~8.27%. The FA-PDA FONs could be stable in a relatively wide pH range and high ionic strength salt solution, and the fluorescence intensities are constant. More importantly, here we developed a method for rapidly selective and sensitive detection of mercury ions (Hg²⁺) within 10 s using FA-PDA FONs based probe, the fluorescence intensities of FA-PDA FONs presented a great linear relationship to Hg²⁺ concentration, the linear range and limit of detection (LOD) were 0-18 µM and 0.18 µM, respectively. Furthermore, the feasibility of the developed Hg²⁺ sensor was verified by determination of Hg²⁺ in mineral water and tap water samples with satisfactory results.

Polyethyleneimine-induced fluorescence enhancement strategy for AIEgen: the mechanism and application

Aggregation-induced emission luminogens (AIEgens) are attracting extensive research attention in the biosensor fields. Herein, we report a new polyethyleneimine (PEI)-induced strategy for enhancing luminescence of TCBPE (an AIEgen) to promote its development in biosensor. The copolymer dots (TCBPE-PEI) with high quantum yield (39.7%) and outstanding stability were synthesized via a one-pot method. The fluorescence enhancement mechanism based on the PEI strategy originated from the restriction of intramolecular motions of TCBPEs and the form of donor-acceptor structures to decrease the inherent energy bandgap. Benefiting from chelating property of TCBPE-PEI by Cu²⁺, a fluorescence-quenching sensor for Cu²⁺ detection was developed based on the fluorescence quenching of the electron transfer effect. Especially, a good linear range of 10-250 nM with a low limit of detection 1.1 nM was achieved, and it was further applied in samples successfully. The current work provides a novel approach to fabricate AIEgen biosensors and shows great potential in Cu²⁺ detection.

Preparation of fluorescein-modified polymer dots and their application in chiral discrimination of lysine enantiomers

Fluorescein-functionalized fluorescent polymer dots (F-PDs) were prepared by a facile one-pot method by magnetic stirring under mild conditions based on carboxymethylcellulose (CMC) and fluorescein as the precursors. The obtained F-PDs exhibited a nanoscale size of 3.2 ± 1.1 nm, excellent water solubility, and bright yellow fluorescence emission with a fluorescence quantum yield of 12.0%. The fluorescent probe displays rapid and sensitive chiral discrimination for lysine focused on different complexation abilities between lysine enantiomers and Cu²⁺. The concentration of L-lysine in the range 4 to 14 mM (R² = 0.997) was measured by the fluorescence intensity ratio (I₅₁₃/I₄₂₉); the exitation wavelength was set to λ_ex = 365 nm. The detection limit was 0.28 mM (3σ/slope). Importantly, this sensor accurately predicted the enantiomeric excess (ee) of lysine enantiomers at the designed concentration (lysine: 20 mM; Cu²⁺: 10 mM) ranges. The proposed sensor was successfully applied to determine L-lys (recovery: 95.8-101%; RSD: 0.465-3.34%) and ee values (recovery: 98.5-102%; RSD: 2.61-3.21%) in human urine samples using the standard addition method.

Accurate identification of kidney injury progression via a fluorescent biosensor array

Identifying the progress of kidney injury may aid the effective treatment and intervention. Herein, we developed a fluorescent biosensor array for instantaneous and accurate identification of the kidney injury progression via "doubled" signals. The multichannel biosensor array consisted of polydopamine-polyethyleneimine (PDA-PEI) and multicolor-labelled different length of DNAs including AAAAA-Cyanine7 (5A-Cy7), AAAAAAAAAA-Texas Red (10A-Texas Red), and AAAAAAAAAAAAAAAAAAAA-VIC (20A-VIC). Facing to the variety of protein in urine with alterable charge accompanied with different progress of kidney injury, the composition of urine replaces the DNA signal molecules, forming their special fluorescence patterns. Taking the size of protein into consideration, the original three variables induced by the protein charge were extended to six variables induced by the two factors of protein particle size and charge difference, which could provide a more accurate strategy to identify the progress of kidney injury. Notably, this strategy not only opened up new perspective for identification the progress of kidney injury via the size and charge of urine protein, but also improved the resolving power of sensor array by increasing the number of sensor elements for extending their potential application to various diseases.

Recent Advances in Intrinsically Fluorescent Polydopamine Materials

Fluorescence nanoparticles have gained much attention due to their unique properties in the sensing and imaging fields. Among the very successful candidates are fluorescent polydopamine (FPDA) nanoparticles, attributed to their simplicity in tracing and excellent biocompatibility. This article aims to highlight the recent achievements in FPDA materials, especially on the part of luminescence mechanisms. We focus on the intrinsic fluorescence of PDA and will not discuss fluorescent reaction with a fluorometric reagent or coupling reaction with a fluorophore, which may cause more in vivo interferences. We believe that intrinsic FPDA presents great potential in bioapplications.

Preparation of fluorescent organic nanoparticles via self-polymerization for tartrazine detection in food samples

Fluorescent polydopamine nanoparticles (PDA NPs) have been effectively synthesized by means of self-polymerization of dopamine under the strong alkaline condition of ethylenediamine at room temperature for 2.5 h.

Preparation of boronic acid-modified polymer dots under mild conditions and their applications in pH and glucose detection

For the first time, boronic acid-modified polymer dots (B-PDs) were fabricated by a "synthesis-modification integration" route using polyethylenimine (PEI) and phenylboronic acid as precursors. Under optimized preparation conditions, the B-PDs exhibited an average size of 2.2 nm, good water solubility, and high fluorescence quantum yield of 8.69%. The B-PDs showed reversible fluorescence response in acid solutions (blue emissions) and alkaline solutions (green emissions). The fluorescence emissions of B-PDs demonstrated an obvious red shift with varying the pH value from 1 - 13. Moreover, glucose could assemble on the surface of B-PDs due to the reversible reaction between boronic acid and cis-diols, which resulted in a blue shift of emission wavelength and an obvious increase of FL intensity at λ_ex = 380 nm based on the aggregation-induced enhancement effect. The glucose sensing method was thus developed in the range 0.0001 - 1.0 mol L^-1. Applications to real human blood and glucose injection samples demonstrated satisfactory results. The B-PDs based on the analytical method display good selectivity, wide detection range, and simplicity in preparation and detection, implying promising applications as a practical platform for biosensing.

A nanosensor for precise discrimination of nephrotoxic drug mechanisms via dynamic fluorescence fingerprint strategy

Drug-induced kidney injury causes structural or functional abnormalities of kidney, seriously affecting clinical practice and drug discovery. However, rapid and effective identification of nephrotoxic drug mechanisms is yet a challenging task arising from the complexity and diversity of various nephrotoxic mechanisms. Herein, we have constructed a polydopamine-polyethyleneimine/quantum dots sensor to instantaneously read out the nephrotoxic drugs mechanisms based on the disparate cell surface phenotypes. Cell surface components induced by multiple nephrotoxic drugs can change the fluorescence emission of multicolor quantum dots, generating their corresponding fluorescent fingerprints. The fluorescence response signatures induced by different nephrotoxic agents are gained with 84% accuracy via linear discriminant analysis. Furthermore, taking the time-toxicity relationship into consideration, dynamic fluorescent fingerprint is obtained through continuous monitoring the progress of renal cell damage, achieving 100% precise classification for nephrotoxic mechanisms of four types of antibiotics. Notably, the fluorescent fingerprint-based high-throughput sensor has been demonstrated by successfully distinguishing nephrotoxic drugs in seconds, employing a promising protocol to discriminate the specific mechanism of nephrotoxic drugs, as well as drug safety evaluation.

Mixing concentrated sulfuric acid and diethylenetriamine at room temperature: A rapid and facile approach to synthesize fluorescent carbon polymer hollow spheres as peroxidase mimics

Fluorescent carbon polymer nanomaterials driven by their important various applications are promising, however, their scalable usages are still hindered by the lack of facile and effective synthesis approaches. Herein, a rapid and facile approach is demonstrated for the preparation of fluorescent carbon polymer hollow spheres (CPHSs), which were synthesized by directly mixing concentrated sulfuric acid (H₂SO₄) and diethylenetriamine (DETA) at room temperature. Notably, both the solid powders and aqueous dispersion of CPHSs possess the fluorescence properties, similar with the reported carbon polymer dots. The formation of CPHSs could be attributed to the polymerization of DETA in the presence of H₂SO₄. The present strategy is universal and fluorescent nanomaterials could also be obtained by using hexamethylenetetramine or polyethylenepolayamine as precursors with the aid of concentrated H₂SO₄. Most importantly, the CPHSs possess peroxidase-like activity and can catalyze oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to its one-electron oxidation product, providing a new method for colorimetric detection of H₂O₂.

A novel copper ion sensing fluorescent probe for fast detection of pyrophosphate and alkaline phosphatase

A Cu²⁺ sensing fluorescent probe is synthesized via a Mannich reaction and is applied in the fluorescence detection of pyrophosphate and alkaline phosphatase.

Nitrogen-Doped Carbon Quantum Dots from Poly(ethyleneimine) for Optical Dual-Mode Determination of Cu2+ and l-Cysteine and Their Logic Gate Operation

In this work, nitrogen-doped carbon quantum dots from poly(ethyleneimine) (PQDs) were synthesized by a low-cost and facile one-step hydrothermal method without other reagents. A quantum yield (QY) of up to 23.2% with maximum emission at 460 nm under an excitation wavelength of 340 nm was ascribed to the high nitrogen doping (20.59%). The PQDs selectively form a blue complex with Cu²⁺ accompanied by strong quenching of the fluorescence emission. Meanwhile, the PQD-Cu²⁺ complex exhibited selective fluorescence recovery and color disappearance on exposure to l-cysteine (Cys). The electron transfer from amino or oxygen groups on the PQDs to Cu²⁺ leads to fluorescence quenching, and a chromogenic reaction of the cuprammonium complex results in a color change. The strong affinity between Cys and Cu²⁺ causes the detachment of Cu²⁺ from the surface of PQDs, so the color of the solution disappears and the fluorescence of PQDs recovers. Under the optimized condition, the proposed sensor was applied to detect Cu²⁺ in the linear range of 0-280 μM. A detection limit of 4.75 μM is achieved using fluorescence spectroscopy and 4.74 μM by monitoring the absorbance variation at 272 nm. For Cys detection, the linear range of 0-800 μM with detection limits of 28.11 μM (fluorescence determination) and 19.74 μM (peak shift determination at 272 nm) was obtained. Meanwhile, the PQD-Cu²⁺ system exhibits distinguishable responses to other biothiols such as l-glutathione (GSH) and dl-homocysteine (Hcy). Based on the multimode signals, an "AND" logic gate was constructed successfully. Interestingly, besides Cu²⁺, Fe³⁺ can also quench the fluorescence of PQDs and the PQD-Fe³⁺ system exhibits superior selectivity for Cys detection. Most importantly, the proposed assay is not only simple, cheap, and stable but also suitable for detecting Cu²⁺ and Cys in some real samples.

One-pot synthesis of fluorescent non-conjugated polymer dots for Fe3+ detection and temperature sensing

The facile preparation of highly fluorescent polymer dots (PDs) still attracts substantial interest. Here, temperature/Fe³⁺ dual-responsive PDs are synthesized under mild conditions via the amidation reaction and self-assembly between hyperbranched polyethyleneimine and 5-aminosalicylic acid. The prepared PDs display strong green fluorescence with quantum yield of 15.5% and 53.3% in water and dimethylsulfoxide, respectively. The PDs also possess unique features, including excellent solubility, solvent polarity-dependent emission, remarkable photostability, as well as good salt-tolerance. Interestingly, the fluorescence intensity of PDs exhibits a reversible and sensitive response to temperature within 20-65 °C, which renders the PDs useful as a thermometer probe. Importantly, Fe³⁺ ion has the specific coordination ability toward the surface groups of PDs, leading to the aggregation and fluorescence quenching of PDs. Thus, the PDs are employed as a fluorescence probe for sensitive detecting Fe³⁺. The fluorescent intensity linearly decreases with increasing Fe³⁺ from 2 to 60 μM. Besides, Fe³⁺ concentration in river water samples is successfully assayed with this developed probe. The non-conjugated PDs with facile preparation, sensitive response to temperature and Fe³⁺ may hold potential applications in environmental monitoring.

Polyethylenimine-Assisted Generation of Optical Nanoprobes for Biosensing Applications

Detection of analytes in biological systems is pivotal to explore their physiological roles and provide diagnostic and treatment options for related diseases, which however remains a great challenge. Optical nanoprobes that exhibit absorption or fluorescence signal changes in response to the targets of interest have emerged as a versatile class of biosensors in the field. Polyethylenimine (PEI) with abundant amine groups plays indispensable roles in the construction of optical nanoprobes and mediating the sensing processes. After interaction with analytes, PEI-based optical nanoprobes can be induced to form aggregates, be disassembled or separated into individual units, or undergo structure/component alterations. As such, the optical properties of these nanoprobes have corresponding changes, allowing for sensitive and selective detection of a wide variety of analytes in biological environment. Up to now, detections of reactive oxygen species, pH, metal ions, biothiols, neurotransmitters, therapeutic agents, oxygen levels, enzyme activities, and virus/bacteria have been successfully demonstrated using PEI-based optical nanoprobes. Herein, we summarize the recent developments of PEI-based optical nanoprobes for biosensing applications and highlight the probe designs and sensing mechanisms. The existing challenges and prospects regarding biosensing applications of PEI-based optical nanoprobes are also briefly discussed.

Integration of Fe3O4 with Bi2S3 for Multi-Modality Tumor Theranostics

The combination of reactive oxygen species (ROS)-induced chemodynamic therapy (CDT) and photothermal therapy (PTT) holds a promising application prospect for their superb anticancer efficiency. Herein, we created a novel Fe₃O₄@polydopamine (PDA)@bovine serum albumin (BSA)-Bi₂S₃ composite as a theranostic agent, by chemically linking the Fe₃O₄@PDA with BSA-Bi₂S₃ via the amidation between the carboxyl groups of BSA and the amino groups of PDA. In this formulation, the Fe₃O₄ NPs could not only work as a mimetic peroxidase to trigger Fenton reactions of the innate H₂O₂ in the tumor and generate highly cytotoxic hydroxyl radicals (•OH) to induce tumor apoptosis but also serve as the magnetic resonance imaging (MRI) contrast agent to afford the precise cancer diagnosis. Meanwhile, the PDA could prevent the oxidization of Fe₃O₄, thus supporting the long-term Fenton reactions and the tumor apoptosis in the tumor. The Bi₂S₃ component exhibits excellent photothermal transducing performance and computed tomography (CT) imaging capacity. In addition, the PDA and Bi₂S₃ endow the Fe₃O₄@PDA@BSA-Bi₂S₃ composite with an excellent photothermal transforming ability which could lead to tumor hyperthermia. All of these merits play the synergism with the tumor microenvironment and qualify the Fe₃O₄@PDA@BSA-Bi₂S₃ NPs for a competent agent in the MRI/CT-monitored enhanced PTT/CDT synergistic therapy. Findings in this research will evoke new interests in future cancer therapeutic strategies based on biocompatible nanomaterials.

Dual-aptamers labeled polydopamine-polyethyleneimine copolymer dots assisted engineering a fluorescence biosensor for sensitive detection of Pseudomonas aeruginosa in food samples

To ensure the food security and protect public health, development of rapid and reliable approaches to detecting foodborne pathogens is of great significance. In this study, polydopamine-polyethyleneimine (PDA-PEI) copolymer dots are prepared via the self-polymerization of dopamine and cross-linking with branched PEI at room temperature. The PDA-PEI copolymer dots are very stable against photobleaching, extreme pH, as well as high ionic strength. They are used as a fluorescent probe to fabricate a biosensor for rapid and sensitive detection and quantification of Pseudomonas aeruginosa (P. aeruginosa). In the biosensor, dual-aptamers of P. aeruginosa are used to label PDA-PEI copolymer dots. Compared to single aptamer labeled PDA-PEI dots, the dual-aptamers labeled PDA-PEI dots endow the biosensor with enhanced sensitivity for target pathogen. The fluorescence biosensor demonstrates a wide linear response to P. aeruginosa in the concentration range of 10¹-10⁷ cfu mL^-1 with acceptable selectivity. The limit of detection is calculated to be 1 cfu mL^-1. The whole detection process can be finished in 1.5 h. The feasibility of the fabricated biosensor is verified by successful determination of P. aeruginosa in skim milk, orange juice, and popsicle samples. The biosensor provides an alternative and attractive platform for rapid and sensitive detection of bacteria in food products.

Au nanoclusters/porous silica particles nanocomposites as fluorescence enhanced sensors for sensing and mapping of copper(II) in cells

In this work, we first report Au nanoclusters/porous silica particles nanocomposites as fluorescence enhanced sensors for selective and sensitive detection of Cu (II). As red-emitting GSH-protected Au nanoclusters (Au NCs) were self-assemble into porous silica particles (PSPs) after ultrasonic treatment. As a result, the Au NCs can be immobilized in the nano-channels of PSPs, which leads to the observation of an immobilized induced emission enhancement phenomenon. The photoluminscence (PL) intensity of the nanocomposites can enhance dozens of times compared with Au NCs. As a result, we obtain a novel PL enhanced sensor of Au NCs/PSPs nanocomposites with excellent PL properties. The as-prepared Au NCs/PSPs nanocomposites show good water-solubility, high stability, low toxicity, and exhibit a high PL quenching for reliable, sensitive and selective detection of Cu²⁺. The limit of detection can reach as low as 1 ppb. What is more, the Au NCs/PSPs nanocomposites also show sensitive detection of Cu²⁺ in living cells. These properties provide the Au NCs/PSPs nanocomposites with promising PL sensors for Cu²⁺ detection in various environmental and biological systems.