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Gold nanostars (GNSs) as a photothermal agent have shown great potential for the treatment of cancers like melanoma. Irradiation of the photothermal agents with light of a suitable wavelength generates heat that induces cellular stress and protein denaturation in cancer cells. The delivery of GNSs to skin using fast dissolving microneedles (MNs) presents a promising approach for painless and convenient administration of the therapy. In this study, polyethylene glycol (PEG) stabilized GNSs able to absorb light in the near‐infra red region and release heat (up to 65 °C, room temperature) are developed. The cytotoxicity of these nanoparticles is assessed before and after exposure to laser irradiation. GNSs show an instant lethal photothermal effect when tested on B16F10 melanoma cells upon irradiation with 808 nm at a power of 800 mW for 10 min. Loading the GNSs in polyvinylpyrrolidone (PVP) MNs preserves the photothermal effect of GNS and the mechanical properties of MNs. GNS‐loaded PVP MNs show efficient piercing in excised porcine skin, fast dissolution in 3 min after insertion and elevation of the skin temperature after laser irradiation (808 nm, 800 mW, 10 min) to 63 °C. Consequently, PEG‐stabilized GNSs and PVP MNs are a promising platform for photothermal therapy in melanoma treatment. [ABSTRACT FROM AUTHOR]

Monitoring an infectious disease early using highly sensitive and non‐invasive techniques is critical for human health. Interestingly, the development of surface‐enhanced Raman scattering (SERS) for biological detection ideally fits these medical requirements and is rapidly growing as a powerful diagnostic tool. SERS can enhance the Raman signal of the target molecule by more than 106 after the adsorption of the molecule on the plasmonic nanostructured surface. This review provides an overview of the use of gold and silver nanoparticles in SERS substrate designs, followed by the development of these SERS substrates in severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) detection. [ABSTRACT FROM AUTHOR]

Paper‐based analytical devices as a low‐cost and point‐of‐care sensing platform have attracted widespread research interest. However, the device fabrication and signal readout remain a challenge for their real‐world applications. Herein, a technically simple paper‐based sensor is developed by taking advantage of the easily accessible paper and the plasmonic property of gold nanomaterials. The sensing mechanism relies on the iodide‐mediated surface etching of gold nanostars that induces a color change from blue to red of the paper strip. The versatility of the paper substrate in size, shape, and materials allows for the facile immobilization of gold nanostars by a simple immersing method, which is easy to operate and free from specialized skills and equipment. In addition, the readout of the paper strip can be conveniently visualized by the naked eye or through a smartphone. This paper‐based sensor advantages in low cost, light weight, easy handling, and disposability that holds great promise as a point‐of‐care detection platform in resource‐constrained settings. [ABSTRACT FROM AUTHOR]

Stretchable electronics (i.e., Elastronics) are essential to the realization of next‐generation wearable bioelectronics for personalized medicine, due to their unique skin‐conformal features ideal for seamless integration with the human body. Significant progress has been made to nanowire‐based elastronics with promising applications ranging from electronic‐skin to advanced energy harvest systems. However, it remains a key challenge to rationally control over the nanowire morphology and configurations to achieve desired multifunctionality. Herein, a stretchable jellyfish‐like gold nanowires film with high conductivity and stretchability is presented by using gold nanostar‐seeded nanowire growth method. They exhibit unique hierarchically oriented structure with gold nanostars as the multi‐branched active sites (top layer) and vertically intertwined nanowires (bottom layer) trailing below the nanostars. Such nanowires film can be stretched up to 200% with a retaining low normalized resistance of 13.8 due to the unique hierarchical structure. Furthermore, the film can be used as stretchable supercapacitor with a 92% capacitance retention and superior durability even after 5000 electrochemical scanning cycles. The method is general, which can be further expanded to other metallic seeds, hence, representing a low‐cost yet efficient strategy for the fabrication of stretchable elastronics and robust energy storage devices for on‐body biosensing and bioelectronics. [ABSTRACT FROM AUTHOR]

In this paper, we report a sensitive surface‐enhanced Raman scattering (SERS) biosensor for the detection of food‐borne pathogens on the basis of recognition of bacterial cells through the specific targeting agent vancomycin. Vancomycin‐functionalized gold nanostars (GNSs–4–MBA–van) were synthesized as SERS tags for specific and sensitive quantification of food pathogens. The Raman reporter molecule 4–mercaptobenzoic acid (4–MBA) was also a linker molecule to attach vancomycin to gold nanostars. The proposed vancomycin‐based SERS technique achieved a detection limit of 5.7 and 8.2 CFU/ml for Staphylococcus aureus and Escherichia coli, respectively. The logarithm of the bacterial concentration ranged from 101 to 107 CFU/ml and demonstrated a linear relationship with the SERS intensity of the characteristic 4–MBA Raman peak at 1,081 cm−1. Principle component analysis was used to discriminate the two pathogens simultaneously by using reproducible and specific intrinsic fingerprints and intracellular components obtained through SERS. Moreover, the spiking tests revealed that GNSs–4–MBA–van is effective as a potential biosensor for detecting pathogens in the fresh meat and food‐processing industries. [ABSTRACT FROM AUTHOR]

Rapid, simple, and reliable detection of toxics at trace level is of great significance for public health. Surface‐enhanced Raman spectroscopy (SERS) as a powerful vibrational spectroscopic technique for molecules probing provides great advantages in trace detection; however, the low reproducibility of SERS signals from spot to spot and substrate to substrate remains a great challenge restricting its real applications. Here, we report a facile method for reproducibly preparing highly uniform self‐assembled monolayers of gold nanostars (Au NSs SAM) as SERS substrates using the classic Langmuir–Blodgett technique and introduced a statistical method to explore the signal reproducibility by t test. Our results show that the Au NSs SAM substrates fabricated in the same batch and different batches generated constant SERS signals without statistical differences and could detect dye molecules CV, R6G, and RhB in solution at concentrations as low as 10−8, 10−8, and 10−7 M, respectively. We then applied the Au NSs SAM for trace detection of Tetracycline (TC), one of the most widespread antibiotics entering the food chain and threatening the ecological balance. A detection limit of 0.05 μg/ml was achieved, with a linear response between SERS signal and TC concentration in the range of 0.05–10 μg/ml. Overall, this uniform Au NSs SAM could be reproducibly fabricated to provide a reliable platform for trace detection of TC residues or other toxics in water and is expected to have broad applications in different fields including environmental monitoring, food security, and so on. [ABSTRACT FROM AUTHOR]

Cancer remains a major health problem that plagues human beings, calling widespread attention to develop novel theranostics to achieve sensitive diagnosis and efficient therapy. Multifunctional nanomedicine that can integrate diagnosis with treatment formulations has been emerging as a powerful strategy to overcome the current drawbacks in conventional clinical cancer treatments. Due to the good biocompatibility, easy surface modification, surface‐enhanced Raman spectroscopy (SERS)/computed tomography (CT)/photoacoustic (PA) imaging properties, and exceptional photothermal performance of gold nanostars (AuNSs), various AuNS‐based complexes or nanohybrids including metal compound/AuNSs, SiO2/AuNSs, polymer/AuNSs, and dendrimer/AuNSs, and so forth have been developed, holding great blueprint in cancer theranostics. Herein, we concisely review the recent progresses in the intriguing design of AuNS‐based nanoplatforms, and their applications in bioimaging, therapy and imaging‐guided cancer treatment, and clarify the possible future perspectives for the design of AuNS‐facilitated cancer theranostics. [ABSTRACT FROM AUTHOR]

Iodide‐mediated surface etching can tailor the surface plasmon resonance of gold nanostars through etching of the high‐energy facets of the nanoparticle protrusions in a rapid and sensitive way. By exploring the underlying mechanisms of this etching and the key parameters influencing it (such as iodide, oxygen, pH, and temperature), we show its potential in a sensitive biosensing system. Horseradish peroxidase‐catalyzed oxidation of iodide enables control of the etching of gold nanostars to spherical gold nanoparticles, where the resulting spectral shift in the surface plasmon resonance yields a distinct color change of the solution. We further develop this enzyme‐modulated surface etching of gold nanostars into a versatile platform for plasmonic immunoassays, where a high sensitivity is possible by signal amplification via magnetic beads and click chemistry. [ABSTRACT FROM AUTHOR]

Precise monitoring of specific biomarkers in biological fluids with accurate biodiagnostic sensors is critical for early diagnosis of diseases and subsequent treatment planning. In this work, we demonstrated an innovative biodiagnostic sensor, portable reusable accurate diagnostics with nanostar antennas (PRADA), for multiplexed biomarker detection in small volumes (~50 μl) enabled in a microfluidic platform. Here, PRADA simultaneously detected two biomarkers of myocardial infarction, cardiac troponin I (cTnI), which is well accepted for cardiac disorders, and neuropeptide Y (NPY), which controls cardiac sympathetic drive. In PRADA immunoassay, magnetic beads captured the biomarkers in human serum samples, and gold nanostars (GNSs) "antennas" labeled with peptide biorecognition elements and Raman tags detected the biomarkers via surface‐enhanced Raman spectroscopy (SERS). The peptide‐conjugated GNS‐SERS barcodes were leveraged to achieve high sensitivity, with a limit of detection (LOD) of 0.0055 ng/ml of cTnI, and a LOD of 0.12 ng/ml of NPY comparable with commercially available test kits. The innovation of PRADA was also in the regeneration and reuse of the same sensor chip for ~14 cycles. We validated PRADA by testing cTnI in 11 de‐identified cardiac patient samples of various demographics within a 95% confidence interval and high precision profile. We envision low‐cost PRADA will have tremendous translational impact and be amenable to resource‐limited settings for accurate treatment planning in patients. [ABSTRACT FROM AUTHOR]

Herein, we report an efficient method to coat gold nanostars with a silica shell of variable thickness and then tunably etch it by using a mild silica etching reagent, NaBH4. This method generates a novel type of nanostar coating in which silica only covers the core, leaving the tips variably exposed. [ABSTRACT FROM AUTHOR]

Gold nanostars with an average tip‐to‐tip length of 52±6 nm were functionalized with different capping agents and used as electrode modification materials for protein electrochemistry. Direct electron transfer between cytochrome c and nanostar‐coated pyrolytic graphite electrodes was observed with the protein in solution. The electrochemical response was improved at nanostars functionalized with a 1 : 1 mixture of 11‐mercaptoundecanoic acid and 4‐mercaptobenzoic acid in comparison with gold nanospheres coated with a similar functionalization. Further immobilization of cytochrome c on pyrolytic graphite while conjugated with the same nanostars guaranteed the maintenance of the protein's native properties, whereas direct adsorption on the bare or nanostar‐modified electrodes resulted in an altered conformational state. The pseudo‐peroxidase activity of the altered cytochrome c was enhanced in the presence of the nanostars. [ABSTRACT FROM AUTHOR]

Abstract: 2D patterns of photothermally responsive near‐infrared (NIR) absorbing gold nanostars (GNS), coated with multiple charged polymer layers, are inkjet‐printed on a glass surface. The shape of the localized surface plasmon resonance (LSPR) NIR absorption bands in the printed patterns loses its peaked form due to plasmon coupling, unless GNS are enveloped in multiple coating layers, keeping the inter‐GNS distance sufficiently large. In the latter case, the photothermal temperature increase (ΔT) induced by the NIR laser irradiation follows a ΔT versus irradiation wavelength (λirr) profile with the same sharply peaked shape of the LSPR bands of the liquid ink. With this result, a new paradigm for inkjet‐writing secure information is introduced, as an alternative to the current methods based on direct visual inspection of printed patterns. While the printed ink patterns of GNS with different coatings are visually indistinguishable despite their different NIR absorption spectrum, their photothermal response changes dramatically with λirr. This allows either to write and read simple information using a single λirr (YES answer for ΔT > threshold) or to use multiple λirr to write and read complex information like thermal bar codes and anti‐counterfeit signatures. [ABSTRACT FROM AUTHOR]

The incorporation of gold nanoparticles in biodegradable polymeric nanostructures with controlled shape and size is of interest toward different applications in nanomedicine. Properties of the polymer such as drug loading and antibody functionalization can be combined with the plasmonic properties of gold nanoparticles, to yield advanced hybrid materials. This study presents a new way to synthesize multicompartmental microgels, fibers, or cylinders, with embedded anisotropic gold nanoparticles. Gold nanoparticles dispersed in an organic solvent can be embedded within the poly(lactic- co-glycolic acid) (PLGA) matrix of polymeric microstructures, when prepared via electrohydrodynamic co-jetting. Prior functionalization of the plasmonic nanoparticles with Raman active molecules allows for imaging of the nanocomposites by surface-enhanced Raman scattering (SERS) microscopy, thereby revealing nanoparticle distribution and photostability. These exceptionally stable hybrid materials, when used in combination with 3D SERS microscopy, offer new opportunities for bioimaging, in particular when long-term monitoring is required. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) light-responsive liposomes are attractive carriers for targeted and controlled drug delivery to the superficial organ or tissue (e.g., skin). This work describes the development of NIR-responsive liposomes by incorporating gold nanostars within liposomes composed of Phospholipon 90 g and cholesterol. Following cellular delivery, photothermal effect around the gold nanostar upon NIR stimulation induces microcavitation and liposome phase transition which consequently triggers the release of encapsulated molecules. Taking GFP plasmid as an example, we demonstrate enhanced gene transfection into fibroblasts following NIR treatment. [ABSTRACT FROM AUTHOR]

We fabricated stable gold nanostars (AuNSs) with tunable extinction properties from the visible spectral region up to 1800 nm, depending on the average values of core size and branch length. The results of their UV-Vis and transmission electron microscopy characterization are compared with computational data from finite elements method, which makes use of an approximated model of the branched structures. The theoretical computations put in evidence the existence of hot spots located on the tips of the nanostars even up to 1800 nm wavelength, which opens the way to the improvement of diagnostics in the IR region. Preliminary Fourier transform Raman experiments performed after functionalization with a fluorescent dye bearing end thiol groups seem to confirm the field enhancing capability of the nanostructures at 1064 nm. [ABSTRACT FROM AUTHOR]

Keywords: gold nanostars; silica etched; NaBH4 B Both surfactant-free and six-branched gold nanostars b can be fully coated by a silica shell by employing a slightly modified Stöber method. Gold nanostars, silica etched, NaBH4, NaBH4. [Extracted from the article]