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Schematic representation of sensing of BNP antigen using the upconversion probe AuNS@Ab@PAA@Mn-NaYF 4 :Yb/Er UCNPs. [Display omitted] • Developed a photon upconversion-based immunoprobe for detecting Brain Natriuretic Peptide (BNP), a heart failure biomarker. • Probe utilizes resonance energy transfer (RET) between Mn2+ ions doped NaYF 4 :Yb/Er upconversion nanoparticles (UCNPs) and gold nanostars (AuNS). • Specific antigen–antibody interactions induce turn-on luminescence response upon BNP detection. • Exhibits high sensitivity with detection range of 30 pg/mL–303 pg/mL and low detection limit of 1.76 pg/mL. • Capable of detecting BNP in human serum within a 10-min incubation with a recovery percentage of 83.76 %–112.94 %. Brain Natriuretic Peptide (BNP) holds significant clinical importance as a biomarker for heart-related conditions aiding in diagnosis, prognosis and monitoring of heart failure, providing valuable insights for timely intercession and patient management. Photon upconversion nanomaterials exhibit captivating ability to convert low energy photons to high energy ones, enabling enhanced sensitivity in sensing application. In this perspective, we develop a new photon upconversion based immunosensor for the detection of a heart failure biomarker, Brain Natriuretic Peptide (BNP) by Resonance Energy Transfer (RET) between Polyacrylic acid capped Mn2+ ions doped NaYF 4 :Yb/Er Upconversion Nanoparticles (PAA@Mn-NaYF 4 :Yb/Er UCNPs) as the donor and gold nanostar (AuNS) as the acceptor. BNP antibody was conjugated on the surface of PAA@Mn-NaYF 4 :Yb/Er UCNPs. The immunosensor can produce strong turn on luminescence intensity in proportional to increasing BNP antigen concentration through specific antigen–antibody interactions. The proposed photon upconversion based immunosensor can achieve turn on behaviour in the linear range from 30 pg/mL to 303 pg/mL with a Limit of Detection (LOD) of 1.76 pg/mL. The immunosensor exhibited appreciable selective and sensitive response towards BNP. [ABSTRACT FROM AUTHOR]

• A highly sensitive star-shaped SERS substrate was synthesized. • A fast and convenient phthalate detection method was proposed. • LSTM model was established to qualitatively and quantitatively analyze phthalates added to EVOO. • A rapid detection of two phthalates was achieved. Phthalates are commonly used plasticizers in the plastics industry, and have received extensive attention due to their reproductive toxicity. Since phthalates are lipophilic solutions, phthalates can easily migrate from packaging to edible oils. This study synthesized stable and sensitive Gold Nanostars as SERS substrates to conduct qualitative and quantitative analysis of two common phthalates, dibutyl phthalate and di(2-ethylhexyl) phthalate. Two ethanol standard solutions and actual oil solutions of phthalates at different concentrations (10, 5, 1, 0.5, 0.1, 0.02 mg/kg) were prepared. After dimension reduction, LSTM achieved the accuracy of 98% for pure EVOO and EVOO adulterated with different types of phthalates. In terms of quantification, LSTM demonstrates great predictive performance with R p 2 greater than 0.97 and the ratio of performance to deviation greater than 5. These results have certain guiding significance for the analysis of plasticizers in edible oil. [ABSTRACT FROM AUTHOR]

[Display omitted] • Using gold nanoparticles as gold seeds, a new type of nanomaterial, gold nanostar, was prepared by seed growth. The dendritic structure on the surface of gold nanostars can produce stronger Raman signal intensity than gold nanoparticles. • A new type of test strip was developed by combining SERS technology with LFA technology to give full play to their unique advantages, such as high sensitivity, no water interference, strong specificity, obvious Raman characteristic peak, simple operation, stable performance and low cost. • The limit of detection for glycinin was 0.23 ng/mL on immunostrips using gold nanostars as immunoprobes.. Glycinin is one of the most nutritious ingredients in soybean, but it is also an allergen that can cause allergic reactions in humans and animals, and even endanger life in severe cases. Therefore, it is imperative to develop a rapid and ultrasensitive detection method for glycinin. In order to achieve this goal, this experiment combined surface-enhanced Raman spectroscopy (SERS) technology with an economical, simple, fast and easy-to-carry immunochromatographic test strip, and successfully constructed an efficient sandwich immunochromatographic test strip. The immunoprobe of the test strip was covalently coupled by gold nanostars (AuNSs), Raman molecule 4-aminothiophenol (4-PATP) and rabbit polyclonal antibody. In this experiment, a gold nanostar immunochromatographic test strip for detecting glycinin was established. The detection limit of the test strip was 0.23 ng / mL, the recovery rate was 91.5–96.6 %, and the coefficient of variation was 1.61–6.15 %. In addition, the test strip had no cross reaction with whey protein, wheat protein, peanut protein, sesame protein and β-conglycinin, indicating that the detection method had good specificity and the ability to avoid false positive results. Hence, this experiment successfully prepared a rapid and sensitive test strip for glycinin. [ABSTRACT FROM AUTHOR]

Highlights • A new bisphenol A detection method using a surface-enhanced Raman scattering lateral flow assay system was developed. • Gold nanoparticles were coated with 4-Aminothiophenol and anti-BPA antibody to serve as a bio-recognition reagent. • The limit of detection for the SERS signals is more sensitive than those of visual intensity. Abstract We report on the development of a new range-extended bisphenol A (BPA) detection method that uses a surface-enhanced Raman scattering lateral flow assay (SERS-LFA) binary system. The assay includes high-SERS-performance gold nanoparticles, i.e., 40 nm gold nanostars (GNSs) and 4-aminothiolphenol (4-ATP) as a Raman reporter. To demonstrate the performance of this SERS-LFA kit in BPA detection, we tested BPA stock solutions with concentrations ranging from 0.05 to 60 ppb. The GNSs were coated with 4-ATP and then anti-BPA antibody serving as a biorecognition reagent to acquire both visual and Raman signals after application in the BPA SERS-LFA kit. The limit of detection for the SERS signals was 0.073 ppb, which is 205 and 20 times more sensitive than those of visual intensity and color intensity quantifications, respectively. The range of quantification of the SERS signals was doubled that of color intensity quantification. The SERS-LFA binary kit successfully detected BPA and provided more accurate results over a broader concentration range (2-fold) than that of optical intensity. [ABSTRACT FROM AUTHOR]

Yolk-shell Au@POP nanocomposites have been constructed and regulated at the atomic level, as high-efficiency electrocatalysts for N 2 -to-NH 3 transformation under mild conditions. [Display omitted] • Yolk-shell Au nanostar@porous organic polymer composites are successfully prepared. • The hydrophobic properties of yolk-shell nanoreactors can be tailored effectively. • Hydrophobic yolk-shell catalysts have excellent electrocatalytic N 2 -to-NH 3 performance. Electrocatalytic nitrogen (N 2) reduction reaction (NRR) is an energy-saving approach to synthesize ammonia (NH 3), which significantly depends on the development of high-efficiency electrocatalysts. Inspired by the catalytic microenvironment of enzymes, a series of yolk-shell nanostructures of monodispersed Au nanostars within porous organic polymers (POPs) have been successfully prepared via a self-sacrificing template strategy. The obtained yolk-shell nanocomposites have highly active Au nanostar cores and permeable POP shells for ambient electrocatalytic NRR to NH 3. The hydrophobic properties of yolk-shell nanoreactors can be tailored accurately by engineering the POP shells at an atomic level, which greatly improves the N 2 fixation performance by inhibiting the hydrogen evolution reaction, resulting in the unprecedented NH 3 yield rate (∼109.1 μg h−1 mg cat. −1) and Faradaic efficiency (∼68.3 %). This work pioneers an effective strategy to construct tailor-made electrocatalysts for the N 2 -to-NH 3 fixation. [ABSTRACT FROM AUTHOR]

Graphene-mediated surface-enhanced Raman scattering (SERS) substrates are currently explored for ultrasensitive detection and expected to provide uniform SERS response by the virtue of graphene and plasmonic metal nanostructures. Here, we integrated graphene oxide (GO) and anisotropic metal nanostructures to create a novel multiple coupling system, in which ultrathin GO as nanospacer was sandwiched between two layers of closely packed gold nanostars (AuNSts). The sandwiched hybrid was prepared through alternative loading of AuNSts and graphene oxide (GO) film via filtration and spin-coating methods in the absence of any polymer stabilizer or organic linkage agent. The morphologies and plasmon resonance of AuNSts could be tuned by simply adjusting the synthesis parameters. Due to the multi-dimensional plasmonic coupling in horizontally and vertically patterned AuNSts, extra chemical enhancement and outstanding molecule harvesting capability from GO interlayer, the as-prepared AuNSt-GO-AuNSt sandwich structures manifested ultrahigh sensitivity and excellent reproducibility (the signal variations <6%). A detection limit of rhodamine-6G (R6G) as low as 10 −13  M and a high enhancement factor of 6.64 × 10 7 were achieved. Particularly, the AuNSt-GO-AuNSt system was applied to detect erythrosine B and chrysoidin down to 10 −9  M as well as offer spectroscopic identification in complicated solutions, indicating great potential practical applications for the rapid and sensitive on-site monitoring, especially for food and environmental safety. [ABSTRACT FROM AUTHOR]

Graphical abstract A versatile nanocomposite was constructed for tumor theranostics, integrating photothermal therapy and self-theranostic caspase-3 imaging. Highlights • A theranostic nanocomposite was constructed, integrating PTT and apoptosis imaging. • Gold nanostar (AuNSs) served as photothermal transducer and also fluorescent quencher. • A caspase-3 responsive peptide was used to conjugate the fluorophore/quencher pair. • AuNS@probe induced cell apoptosis, giving enhanced PTT efficiency. • Turning-on caspase-3 imaging served as self-theranostic feedback for apoptosis monitoring. Abstract We demonstrated a novel nanocomposite based on fluorescent turn-on gold nanostars for simultaneous tumor targeting photothermal therapy (PTT) and feedback apoptosis imaging of the self-therapeutic effect. In this theranostic agent (AuNS@probe), gold nanostars (AuNSs) and fluorescent dye Atto 655, as a fluorophore/quencher pair, were conjugated to form intermolecular fluorescence quenching in virtue of the linkage of a caspase-3 responsive peptide. Folic acid targeting moiety facilitated the selective accumulation in cancer cells via receptor-mediated endocytosis. Upon photo irradiation, AuNS@probe demonstrated excellent photothermal effect and induced cell death with apoptosis related mechanism. The typical apoptosis-effector proteases, caspase-3, was subsequently activated and terminated intramolecular fluorescent quenching process. Obvious fluorescence recovery could be applied to precisely assess the activated caspase-3 expression and the real time therapeutic efficacy. This novel versatile nanocomposite could serve as a theranostic agent for tumor targeting PTT and also provide self-therapeutic monitoring for precise cancer therapeutic applications. [ABSTRACT FROM AUTHOR]

Light-triggered nanotheranostics opens a fascinating but challenging avenue to achieve simultaneous and highly efficient anticancer outcomes for multimodal therapeutic and diagnostic modalities. Herein, a multifunctional phototheranostics based on a photosensitizer-assembled graphene/gold nanostar hybrid (GO/AuNS-PEG) was developed for cancer synergistic photodynamic (PDT) and photothermal therapy (PTT) as well as effective photothermal imaging. The stable and biocompatible GO/AuNS-PEG composite displayed a high photothermal conversion efficiency due to the enhanced optical absorbance of both graphene and gold nanostars in the near-infrared (NIR) range. By tuning the absorption wavelength of GO/AuNS-PEG to that of Chlorin e6 (Ce6), GO/AuNS-PEG/Ce6 completely eliminated the EMT6 xenograft tumors by the tremendous synergistic anticancer efficiency of simultaneous PDT and PTT under a single NIR laser irradiation (660 nm) in vivo . The underlying mechanism may be the enhanced cytoplasmic uptake and accumulation of GO/AuNS-PEG/Ce6 and the subsequent photodestruction of the lysosomal membrane and mitochondria. Moreover, GO/AuNS-PEG/Ce6 exhibited negligible side-effects on the body and other organs. These results demonstrate that the graphene/gold nanostar nanoconstruct provides a versatile and reliable integrated platform for the photo-controlled cancer theragnostic applications. Statement of Significance This work demonstrated the application of graphene-Au Nanostars hybridized system (denoted as GO/AuNS-PEG) in single wavelength laser induced synergistic photodynamic (PDT) and photothermal therapy (PTT) and effective cancer photothermal/fluorescence multimode imaging. GO/AuNS-PEG showed excellent biocompatibility and high dual-enhanced photothermal efficiency under the near-infrared laser irradiation that was very promise for deep tumor imaging. By combining with the photosensitizer Chlorin e6, both in vitro and in vivo data confirmed the efficient photoablation of the EMT6 tumors through the synergistic PDT and PTT effect under the activation of a single wavelength laser. [ABSTRACT FROM AUTHOR]

In this work, mitochondria-targeting gold nanostar (AuNS) and anticarcinogen DOX were co-encapsulated in hyaluronic acid (HA) protective shell for tumor-targeting synergistic photothermal/chemo-therapy. Cationic peptide R 8 and mitochondria-targeting pro-apoptotic peptide TPP-KLA were co-decorated on AuNS to form AuNS-pep via Au-S bonds. Then, electronegative HA was further coated on the surface via electrostatic interaction for cancer cell targeting. During the coating process, DOX was also introduced via electrostatic interaction to obtain a versatile nanoplatform AuNS-pep/DOX@HA. It was found that the nanoplatform could be internalized into tumor cells via CD44 receptor-mediated recognition. Followed digestion by hyaluronidase (HAase), the therapeutic nanoplatform was able to release DOX for chemotherapy and mitochondria-targeting nanoheater AuNS-pep for near infrared (NIR) light triggered subcellular photothermal therapy (PTT). This tumor-targeting nanoplatform AuNS-pep/DOX@HA displayed prominent non-resistant or resistant tumor inhibition both in vitro and in vivo . [ABSTRACT FROM AUTHOR]

Bacterial pathogens represent a safety concern in the food industry, and this is amplified by the lack of sensing devices that can be applied on-site by non-trained personnel. In this study, peroxidase-mimicking activity of gold nanostars was exploited to develop a user-friendly colourimetric sensor. A smartphone was exploited as an image reader and analyser, empowered with a novel App developed in-house. The mobile App was evaluated and compared with a commercial smartphone App for its capability to quantify generated colourimetric signals. A major obstacle found with sensors relying on gold nanozymes is the fact that modification of the surface of gold nanoparticles with biorecognition elements generally lead to a suppression of their nanozyme activity. This drawback was overcome by introducing an autocatalytic growth step, which successfully restored the peroxidase-mimicking activity through generation of new gold nanoseeds acting as catalytic centres. A proof-of-concept using this sensing mechanism was developed targeting Mycobacterium bovis , a zoonotic pathogen primarily found in cattle but that can be transmitted to humans by consumption of contaminated food and cause tuberculosis disease. The resulting smartphone-based immunological sensor has shown promising results with a linear response between 104 – 106 CFU/mL, enabling detection of M. bovis at concentrations as low as 7.2·103 CFU/mL in buffer conditions. It is anticipated that the concept of the developed approach will have applicability in many fields relying on smartphone-based biosensing. [ABSTRACT FROM AUTHOR]

Graphene aerogel has attracted increasing attention due to its large specific surface area, high-conductivity and electronic interaction. The paper reported a facile synthesis of nitrogen-doped multiple graphene aerogel/gold nanostar (termed as N-doped MGA/GNS) and its use as the electrochemical sensing platform for detection of double stranded (dsDNA). On the one hand, the N-doped MGA offers a much better electrochemical performance compared with classical graphene aerogel. Interestingly, the performance can be enhanced by only increasing the cycle number of graphene oxide gelation. On the other hand, the hybridization with GNS further enhances the electrocatalytic activity towards F e ( C N ) 6 3 − / 4 − . In addition, the N-doped MGA/GNS provides a well-defined three-dimensional architecture. The unique structure make it is easy to combine with dsDNA to form the electroactive bioconjugate. The integration not only triggers an ultrafast DNA electron and charge transfer, but also realizes a significant synergy between N-doped MGA, GNS and dsDNA. As a result, the electrochemical sensor based on the hybrid exhibits highly sensitive differential pulse voltammetric response (DPV) towards dsDNA. The DPV signal linearly increases with the increase of dsDNA concentration in the range from 1.0×10 − 21 g ml − 1 to 1.0×10 −16 g ml −1 with the detection limit of 3.9×10 −22 g ml −1 ( S / N =3). The sensitivity is much more than that of all reported DNA sensors. The analytical method was successfully applied in the electrochemical detection of circulating free DNA in human serum. The study also opens a window on the electrical properties of multiple graphene aerogel and DNA as well their hybrids to meet the needs of further applications as special nanoelectronics in molecule diagnosis, bioanalysis and catalysis. [ABSTRACT FROM AUTHOR]

Gold nanomaterials promise a wide range of potential applications in chemical and biological sensing, imaging, and catalysis. In this paper, we demonstrate a facile method for room-temperature synthesis of gold nanostars (AuNSs) with a size of ~50 nm via seeded growth. Significantly, the AuNSs are found to have high light-scattering properties, which are successfully used as labels for sensitive and selective detection of nucleic acids and proteins by using exonuclease III (Exo III) as a biocatalyst. For DNA detection, the binding of targets to the functionalized AuNS probes leads to the Exo III-stimulated cascade recycling amplification. As a result, a large amount of AuNSs are released from magnetic nanoparticles (MNPs) into solution, providing a greatly enhanced light-scattering signal for amplified sensing process. Moreover, a binding-induced DNA three-way junction (DNA TWJ) is introduced to thrombin detection, in which the binding of two aptamers to thrombin triggers assembly of the DNA motifs and initiates the subsequent DNA strand displacement reaction (SDR) and Exo III-assisted cascade recycling amplification. The detection limits of 89 fM and 5.6 pM are achieved for DNA and thrombin, respectively, which are comparable to or even exceed that of the reported isothermal amplification methods. It is noteworthy that based on the DNA TWJ strategy the sequences are independent on target proteins. Additionally, the employment of MNPs in the assays can not only simplify the operations but also improve the detection sensitivity. Therefore, the proposed amplified light-scattering assay with high sensitivity and selectivity, acceptable accuracy, and satisfactory versatility of analytes provides various applications in bioanalysis. [ABSTRACT FROM AUTHOR]

This review focuses on colorimetric and visual assays for determination of mercury(II) (Hg 2+ ) ions based on gold nanoparticles (AuNPs), fluorescent gold nanoclusters (AuNCs), gold nanorods (AuNRs), gold nanoflowers (AuNFs) and gold nanostars (AuNSs). The analytical colorimetric approaches based on AuNPs can be categorized according to the aggregation or disaggregation mechanisms of functionalized or unmodified AuNPs. The colorimetric concept involves change of the color of a solution of AuNPs from deep red to purple or blue. Disaggregation assays involve reversing the color from blue to red. Detection using AuNCs is based on Hg 2+ -induced fluorescence quenching of functionalized AuNCs and label-free AuNCs. The benefits of these systems are simplicity, rapidity, cost-effective production, ease of usage, easy visualization of the color change, and detection using spectrophotometry, fluorometry and the naked eye. We summarize applications to real samples, limits of detection, and the development of test strips. [ABSTRACT FROM AUTHOR]

Abstract: Paper-based SERS active substrates were prepared adsorbing spherical and star-shaped gold nanoparticles on a standard filter paper support. Besides the deposition conditions, morphological parameters of the particles were found to strongly affect the enhancer properties of the substrates. The developed substrate was tested regarding surface homogeneity as well as in the quantitative analysis of malachite green, – a well documented Raman reporter dye – and proved to be capable also to detect the oxidation products of apomorphine, a well-known drug molecule used in Parkinson's disease. This material is simple to prepare, easy to handle and dispose and as such it could be a perfect target for further development of a new family of mass-produced, cheap solid SERS substrates. [Copyright &y& Elsevier]

• Cellulose nanofiber-based SERS wipers were fabricated on quartz papers. • Wipers were coated with a mixture of AgNP and AuNS. • A "drop-wipe-test" protocol was developed for rapid detection of pesticide residues. • The detection limit for ferbam on kale leaves was 50 μg/kg. • CNF-based SERS/wiper method can be use to detect pesticides in fresh produce. This study developed a novel surface-enhanced Raman spectroscopy (SERS) method coupled with cellulose nanofiber (CNF)-based SERS wipers that were fabricated on quartz papers coated with a mixture of silver nanoparticle (AgNP) and gold nanostar (AuNS). A "drop-wipe-test" protocol was developed for rapid detection of pesticide residues in vegetables by SERS. Tremendously enhanced Raman scattering signals were obtained from the quartz/CNF/mixture (AgNP + AuNS) substrate, which were much higher than the paper/mixture (AgNP + AuNS) substrate. This method was used to detect ferbam on kale leaves within a few minutes and the detection limit was 50 μg/kg based on the PLS models (R2 = 0.89). The enhancement factor of the SERS substrate was calculated to be ~ 104 with satisfactory reproducibility. Satisfactory SERS performance could be achieved within 1-month storage period. These results demonstrate that this CNF-based SERS/wiper method is a practical approach for rapid detection of chemical contaminants in fresh produce. [ABSTRACT FROM AUTHOR]

The sensitivity for analytes of interest is vital for environment protection and food safety. Here, we propose an extremely sensitive assay toward Pb2+ by using gold nanostars (GNSs) as probes based on the catalytic activity of Pb on etching gold atoms after being reduced in the presence of 2-mercaptoethanol (2-ME) and sodium thiosulfate. GNSs were prepared by using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid as both the reducing and capping agents, enabling high stability and sensitivity for quantitation of Pb2+. Upon increasing Pb2+ concentration over the range of 0–10 μM, GNS solution color changed from greenish-blue to blue to purple to red, and eventually to colorless. The color change can be distinguished by naked eye at the Pb2+ concentration as low as 200 pM. Through monitoring longitudinal localized surface plasmon of GNSs, Pb2+ could be detected with a limit of detection of 1.5 pM, and the working range is 2 pM-1 μM. The ultra-high sensitivity of our assay stems from the high catalysis of Pb on etching gold on tips and branches in the presence of 2-ME and sodium thiosulfate, leading to the shape deformation to spherical gold nanoparticle and the corresponding significant changes in their optical properties. The assay provides high selectivity of Pb2+ over the tested interfering metal ions like Cu2+. With high sensitivity and selectivity, the assay was efficiently validated by analyzing water samples and monitoring the migration of Pb2+ from the tested container to water. An ultrasensitive colorimetric assay for picomolar detection of lead ion by using gold nanostars is proposed. [Display omitted] • Gold nanostars (GNSs) with unique optical properties show great potentials as probes for sensitively detecting analytes. • An ultrasensitive assay for detecting picomolar Pb2+ is proposed by using GNSs. • The assay is based on the catalyst of Pb on etching GNSs by 2-mercaptoethanol and Na 2 S 2 O 3. • The sensitive assay is valuable to investigate lead migration from food packages to waters. [ABSTRACT FROM AUTHOR]

• An electrochemical oxidation-assisted complexation strategy was first proposed. • A novel colorimetric sensor for highly selective detection of SCN− was developed. • A wide detection range for SCN− (10 nM to 80 mM) was obtained. • High affinity between SCN− and ZnPc contribute to improve the selectivity. In this work, we developed an electrochemical oxidation-assisted complexation strategy for highly sensitive and selective detection of thiocyanate (SCN−). Gold nanostars (AuNSs) with uniform and sharp tips were first prepared, and we found they can be quickly etched to gold nanoparticles (AuNPs) under electrochemical oxidation with the existence of halide and halogen-like ions. Through introducing SCN−-selective molecule: zinc phthalocyanine (ZnPc), the fabricated ZnPc-AuNSs/ITO electrode can rapidly and selectively response to SCN− under electrochemical oxidation, manifesting as a noticeable change in color from navy blue to red. Thus SCN− concentration can be easily reflected. The wide wavelength tuning range of AuNSs to AuNPs make the ZnPc-AuNSs/ITO sensor obtain a much wider detection range for SCN− (10 nM to 80 mM) than most other reported studies. In addition, the detection limit is as low as 3 nM. It renders the sensor to be easily used in much diluted matrixes, which can further lower the interference. We further applied the colorimetric sensor to SCN− detection in wastewater and milk, excellent performance was obtained. The proposed electrochemical oxidation-assisted complexation strategy will have good promise in developing colorimetric sensors with high selectivity and wide detection range, and will display more useful application in environmental monitoring. [ABSTRACT FROM AUTHOR]