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Abstract This study reports on the facile development of star-shaped gold nanoparticles via seed-mediated growth protocol. Gold nanostars (AuNSTs) demonstrated average particle size of 48 nm using transmission electron microscopy (TEM). Chemical composition of AuNSTs was verifired using energy dispersive X-ray spectroscopy (EDX) mapping. AuNSTs demonstrated high optical response under visible spectrum, with maximum absorption at 685 nm, using UV-Vis spectroscopy. Therefore AuNSTs could be involoved into photocatalytic reaction under visible spectrum. AuNSTs demonstrated superior performance in degradation of rhodamine B dye (RB), and disinfection of some pathogenic bacteria. AuNSTs offered enhanced removal efficiency against rhodamine B dye (82.0 ± 0.35% in 135 min) under visible irradiation. Remarkably, under proper conditions of pH = 9, approximately 94 ± 0.55% of a 10 ppm RB solution was effectively photodegraded after 135 min; this could be ascribed to the strong electrostatic attraction between negatively charged AuNSTs surface and positive RB contaminant. This superior photocatalytic activity of AuNSTs could be correlated to high interfacial charge transfer efficiency for Au, and enhanced charge pair separation under visible spectrum. Additionally, AuNSTs exhibited potential antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). AuNSTs demonstrated substantial antibacterial activity via disk diffusion and microbroth dilution tests with zones of inhibition and minimum inhibitory concentrations (MIC) for E. coli (20.0 ± 0.54 mm, 1.25 µg/ml) and S. aureus (23.0 ± 0.35 mm, 0.625 µg/ml), respectively. In conclusion, AuNSTs demonstrated efficient dye removal capabilities along with significant antimicrobial activity against gram-positive and gram-negative bacterial strains.

The development of highly sensitive and specific diagnostic tools is crucial for the early detection and treatment of cancer. Aptamer-conjugated gold nanostars (AuNSs) offer a promising approach, combining molecular recognition with unique plasmonic properties for targeted detection of cancer biomarkers. In this study, we developed a colorimetric biosensor based on S2.2 aptamer-conjugated AuNSs for detecting mucin 1 (MUC1)-positive lung and breast cancer cells. The detection principle hinges on the specific binding of the S2.2 aptamer to the MUC1 protein, which is overexpressed on the surface of cancer cells. Upon binding of the S2.2 aptamer to mucin 1 (MUC1), the aggregation of AuNSs occurs, leading to concentration-dependent changes in their optical properties that are visible as a color change. The biosensor demonstrated high sensitivity, detecting MUC1-positive cells within a range of 500 to 20 000 cells per well, with a detection limit of 450 cells per well in water and serum media. The simplicity of the colorimetric response, coupled with label-free detection, highlights the potential of this biosensor for point-of-care applications. [ABSTRACT FROM AUTHOR]

In the pursuit of advancing molecular sensing through surface-enhanced Raman spectroscopy (SERS), the combination of plasmonic nanoparticles and metal-organic frameworks (MOFs) has emerged as a highly effective approach to enhance the sensitivity and selectivity of SERS substrates. However, most prior investigations have predominantly focused on MOF-coated plasmonic nanoparticles in core@shell or layer-by-layer configurations, leaving a notable knowledge gap in exploring alternative configurations. Herein we present a facile method to construct a particle-on-mirror architecture by selectively coating a MOF, zeolitic imidazolate framework-8 (ZIF-8), onto the tips of Au nanostars and subsequently depositing the resultant nanoparticles onto a Au film. This design integrates the electric field enhancement at the sharp tips and nanogaps, along with the molecular enrichment function within the porous MOF immobilized at the tips and nanogaps, leading to a substantial boost in the SERS signal intensity. Such a unique SERS platform enables consistent and outstanding SERS performance for analytes of different sizes. This work opens up a promising strategy for constructing multifunctional nanostructures for sensitive SERS detection in real-life scenarios. [ABSTRACT FROM AUTHOR]

Monitoring the progression of Alzheimer's disease (AD) is crucial for mitigating dementia symptoms, alleviating pain, and improving mobility. Traditionally, AD biomarkers like amyloid plaques are predominantly identified in cerebrospinal fluid (CSF) due to their concentrated presence. However, detecting these markers in blood is hindered by the blood–brain barrier (BBB), resulting in lower concentrations. To address this challenge and identify pertinent AD biomarkers—specifically amyloid plaques and apolipoprotein E4 (ApoE4)—in blood plasma, we propose an innovative approach. This involves enhancing a screen-printed carbon electrode (SPCE) with an immobilization matrix comprising gold nanostars (AuNSs) coated with chitosan. Morphological and electrical analyses confirmed superior dispersion and conductivity with 0.5% chitosan, supported by UV–Vis spectroscopy, cyclic voltammetry, and Nyquist plots. Subsequent clinical assays measured electrical responses to quantify amyloid-β 42 (Aβ42) (15.63–1000 pg/mL) and APoE4 levels (0.41 to 40 ng/mL) in human blood plasma samples. Differential pulse voltammetry (DPV) responses exhibited peak currents proportional to biomarker concentrations, demonstrating high linear correlations (0.985 for Aβ42 and 0.919 for APoE4) with minimal error bars. Cross-reactivity tests with mixed solutions of amyloid-β 40 (Aβ40), Aβ42, and ApoE4 indicated minimal interference between biomarkers (<3% variation), further confirming the high specificity of the developed sensor. Validation studies demonstrated a strong concurrence with the gold-standard enzyme-linked immunosorbent assay (ELISA), while interference tests indicated a minimal variation in peak currents. This improved device presents promising potential as a point-of-care system, offering a less invasive, cost-effective, and simplified approach to detecting and tracking the progression of AD. The substantial surface binding area further supports the efficacy of our method, offering a promising avenue for advancing AD diagnostics. [ABSTRACT FROM AUTHOR]

Convenient, rapid, highly sensitive and on-site iron determination is important for environmental safety and human health. We developed a sensing system for the detection of Fe(III) in water based on 7-mercapto-4-methylcoumarine (MMC)-stabilized silver-coated gold nanostars (GNS@Ag@MMC), exploiting a redox reaction between the Fe(III) cation and the silver shell of the nanoparticles, which causes a severe transformation of the nanomaterial structure, reverting it to pristine GNSs. This system works by simultaneously monitoring changes in the Localized Surface Plasmon Resonance (LSPR) and Surface-Enhanced Raman Spectroscopy (SERS) spectra as a function of added Fe(III). The proposed sensing system is able to detect the Fe(III) cation in the 1.0 × 10−5–1.5 × 10−4 M range, and its selectivity of the GNS@Ag@MMC sensor toward iron has been verified monitoring the LSPR and the SERS response to other cations with a clear selectivity toward Fe(III). [ABSTRACT FROM AUTHOR]

A reduced polyoxometalate (POM) functionalized with bisphosphonate (BP) ligands possessing antitumoral properties was used to synthesize metallic gold nanostars (AuNSs) with high reproducibility through a silver-assisted seed growth method. Notably, this study is the first to employ a reduced polyoxometalate as a dual-function reducing and capping agent in the synthesis of gold nanostars. The resulting AuNS@POM composites, characterized by a plasmon band located at 744 nm, combine in a single hybrid nanocomposite alendronate ligands, Mo-(VI) ions, and Au0 centers. The colloidal stability of AuNS@POM was demonstrated in a biological culture medium, and cell experiments were performed to study its antitumoral activity on U87 and MCF7 cell lines from glioblastoma and liver cancer, respectively. First, it was established that the antitumoral activity of the BP POM is enhanced due to the Mo-(V) to Mo-(VI) oxidation process that occurs during AuNS formation. Second, it has been shown that in the presence of the composite, cellular metabolic activity decreases drastically under the effect of irradiation at 808 nm, even leading to almost complete cell death. AuNS@POM therefore exhibits strong antitumor chemo–photothermal activity, paving the way for the development of a type of dual therapeutic agent operating under near-infrared irradiation. [ABSTRACT FROM AUTHOR]

We developed an unconventional seed-mediated in situ synthetic method, whereby gold nanostars are formed directly on the internal walls of microfluidic reactors. The dense plasmonic substrate coatings were grown in microfluidic channels with different geometries to elucidate the impacts of flow rate and profile on reagent consumption, product morphology, and density. Nanostar growth was found to occur in the flow-limited regime and our results highlight the possibility of creating shape gradients or incorporating multiple morphologies in the same microreactor, which is challenging to achieve with traditional self-assembly. The plasmonic-microfluidic platforms developed herein have implications for a broad range of applications, including cell culture/sorting, catalysis, sensing, and drug/gene delivery.

Gold nanostars have shown enormous potential as the main enablers of advanced applications ranging from biomedicine to sensing or catalysis. Their unique anisotropic structure featuring sharp spikes that grow from a central core offers enhanced optical capabilities and spectral tunability. Although several synthesis methods yield NSs of different morphologies and sizes up to several hundred nanometers, obtaining small NSs, while maintaining their plasmonic properties in the near-infrared, has proven challenging and elusive. Here, we show that Cu2+ addition during NS synthesis in polyvinylpyrrolidone/dimethylformamide generates more crystallographic defects and promotes the directional growth, giving rise to NSs with a larger number of much sharper spikes. They are also formed at smaller volumes, enabling the generation of ultrasmall nanostars, with a volume as small as 421 nm3 (i.e., 9.2 nm of volume-equivalent diameter), while maintaining a plasmon resonance in the near-infrared. To this end, we systematically evaluate the influence of synthesis parameters on the nanostar size and optical characteristics and demonstrate their properties for applications in catalysis, surface-enhanced Raman spectroscopy sensing, and hyperthermia. The ultrasmall nanostars show excellent attributes in all of them, leveraging their small size to enhance properties related to a higher surface-to-volume ratio or colloidal diffusivity. [ABSTRACT FROM AUTHOR]

This study presents the development of an affordable and straightforward solution-based surface-enhanced Raman scattering (SERS) detection platform, employing plasmonic-active silver–gold nanostars coated with graphene oxide (GO-SGNS). The inclusion of GO with SGNS produced several advantages, including colloidal stability, SERS detection reproducibility, and improved sensitivity. The solution-based SERS platform exhibited an ultralow detection capability with high reproducibility, and we achieved the limit of detection (LOD) as low as 10, 50, 100, and 100 pM for the pesticides-ziram, phorate, triazophos, and azinphos-methyl, respectively. To illustrate the potential for food safety, the surfaces of apples were pretreated with pesticides and were directly analyzed without any sample pretreatment. Furthermore, the solution-based SERS platform provided rapid detection of the four pesticides in binary and quaternary mixtures on apple surfaces, indicating good feasibility and multiplex capability of the method. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) is a powerful molecular spectroscopy technique that combines Raman spectroscopy with nanostructured metallic surfaces to amplify the Raman signals of target molecules by more than 103. The high sensitivity of SERS poses a significant opportunity for pesticide detection in complex matrices at ultralow concentrations. In this study, we improved the SERS sensitivity for imidacloprid (IMD) by employing silver nanostars (AgNs) coated with gold nanostars (AuNs) as the SERS-active substrate. The SERS response towards IMD detection increased based on the combination of AuNs and AgNs on the substrate surface. The intensity of the SERS signal of IMD using the AuNs/AgNs substrate increased compared to using individual metal nanoparticle substrates. The excellent reproducibility of SERS intensity using the AuNs/AgNs substrate was achieved with a low relative standard derivative (RSD) of 4.87% for 20 different spots on the same sample and 5.19% for 20 different samples. This detection system can be used for multiple tests, which is crucial for the advancement of handheld sensors designed for field use, where minimal or no high-level technical support is accessible. This manuscript reports the first introduction of gold nanostars on silver nanostars surface as the Surface-enhanced Raman spectroscopy (SERS) active elements to increase the SERS response towards imidacloprid pesticide. This combination of two metal nanostars showed an enhancement in imidacloprid signal at low concentrations on the AuNs/AgNs surface when compared to the signal on the surface composed of a single type of metal nanostars. The substrates were shown to be stable over a month in storage and can be reused many times. (Image credit: N. Abu Bakar.) [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) substrate composed of nanocellulose-gold nanostars (S-CNF/Au NSs) was prepared, which exhibited remarkable homogeneity and stability. P-aminothiophenol (PATP) was modified on the S-CNF/Au NSs substrate by Au–S bonds. The amino group of PATP was utilized to react with the aldehyde group of malondialdehyde (MDA) in a Schiff base reaction, resulting in a new Raman peak at 1655 cm−1 attributed to C = N vibration. Since the intensity of the Raman peak at 1078 cm−1 was hardly affected under acidic conditions, the ratio of the characteristic peak of C = N (1655 cm−1) to the peak intensity at 1078 cm−1 was used as a characterization of the MDA concentration. The precision of signal intensity was further corrected to improve confidence of the results. The developed SERS sensing system displayed satisfactory sensitivity with a linear detection range of 1 × 10–9 ~ 2.5 × 10–2 mM and a limit of detection (LOD) of 1.29 × 10–11 mM. The S-CNF/Au NSs 2D substrate was able to sensitively differentiate serum from gastric cancer patients and healthy individuals by SERS analysis (p < 0.0001), which was superior to colorimetric analysis (p < 0.01). This result suggests that the proposed S-CNF/Au NSs 2D substrate has potential for MDA detection and can be used for early diagnosis of gastric cancer. [ABSTRACT FROM AUTHOR]

Monitoring the progression of Alzheimer’s disease (AD) is crucial for mitigating dementia symptoms, alleviating pain, and improving mobility. Traditionally, AD biomarkers like amyloid plaques are predominantly identified in cerebrospinal fluid (CSF) due to their concentrated presence. However, detecting these markers in blood is hindered by the blood–brain barrier (BBB), resulting in lower concentrations. To address this challenge and identify pertinent AD biomarkers—specifically amyloid plaques and apolipoprotein E4 (ApoE4)—in blood plasma, we propose an innovative approach. This involves enhancing a screen-printed carbon electrode (SPCE) with an immobilization matrix comprising gold nanostars (AuNSs) coated with chitosan. Morphological and electrical analyses confirmed superior dispersion and conductivity with 0.5% chitosan, supported by UV–Vis spectroscopy, cyclic voltammetry, and Nyquist plots. Subsequent clinical assays measured electrical responses to quantify amyloid-β 42 (Aβ42) (15.63–1000 pg/mL) and APoE4 levels (0.41 to 40 ng/mL) in human blood plasma samples. Differential pulse voltammetry (DPV) responses exhibited peak currents proportional to biomarker concentrations, demonstrating high linear correlations (0.985 for Aβ42 and 0.919 for APoE4) with minimal error bars. Cross-reactivity tests with mixed solutions of amyloid-β 40 (Aβ40), Aβ42, and ApoE4 indicated minimal interference between biomarkers (

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) peptides in the brain. Among the different forms of Aβ, oligomers (Aβo) are considered the most toxic and have been implicated in AD pathology. However, the accurate detection of Aβo remains challenging due to their low abundance and structural complexity. In this study, we propose an electrochemical sensing platform based on gold nanostars (AuS) for the detection of Aβo in AD. The AuS were functionalized with a peptide probe (PrPc) that specifically interacts with Aβo. The PrPc-AuS sensing platform exhibited high sensitivity and selectivity for Aβo detection. The electrochemical impedance spectroscopy (EIS) analysis showed significant changes in impedance upon binding of Aβo to the PrPc-AuS surface, providing quantitative information about the Aβo concentration. The platform demonstrated a linear detection range of 5–200 pM with a detection limit of 2 pM, meeting the requirements for clinical detection. This electrochemical sensing platform offers a promising approach for the early diagnosis and monitoring of AD, contributing to the development of point-of-care diagnostics for neurodegenerative diseases.

A high-throughput surface-enhanced Raman scattering (SERS)-sensing platform is presented for FNT detection in human urine without any sample preparation. The sensing platform is based on plasmonics-active silver-coated sharply branched gold nanostars (SGNS). The effect of silver thickness was investigated experimentally and theoretically, and the results indicated that SERS enhancement was maximum at an optimum silver thickness of 45 nm on the sharply spiked SGNS. The proposed high-throughput SERS platform exhibited ultrahigh sensitivity and excellent enhancement uniformity for a model analyte, i.e., crystal violet. Moreover, the SERS-sensing platform demonstrated good sensitivity of FNT spiked in human urine samples with two differential linear response ranges of 2 to 0.2 µg/mL and 0.1 µg/mL to 100 pg/mL, respectively, with a detection limit as low as 10.02 pg/mL. The spiked human urine samples show satisfactory recovery values from 92.5 to 102% with relative standard deviations (RSD) of less than 10%. In summary, the high-throughput performance of the proposed microplate-based SERS platform demonstrated great potential for rapid low-cost SERS-based sensing applications. [ABSTRACT FROM AUTHOR]

Gold nanostars (AuNSs) have achieved special relevance for potential biomedical applications, e.g., in theranostics. In relation to this, some authors have explored controlling the conditions that trigger structural and morphological changes in these structures. In this work, we studied conditions that can trigger morphological changes of AuNSs or maintain their stability, such as ligand exchange to nonthiolated and thiolated species. First, the synthesis stabilizing ligand of AuNS, 4-(2-hydroxyethyl)-1-piperazinapropanesulfonic acid (EPPS), was exchanged for nonthiolated species to trigger or prevent morphological changes. One of these species, triphenylphosphine-monosulfonate (TPPMS), generated a stable and unexplored nanostructure even at acidic pH, with interaction mediated mainly by aromatic groups and the phosphine moiety, in comparison to hexadecyltrimethylammonium bromide (CTAB) and citrate, which are ligands that trigger morphological changes of AuNS. Moreover, TPPMS-coated AuNSs can be exchanged by thiolated species, such as carboxylated poly-(ethylene glycol) (HS-PEG-COOH), offering more versatility through covalent strategies. In addition, properties related to the application of these stabilized AuNSs were explored, such as photothermia and biocompatibility. The photothermal transduction efficiency and cell viability of AuNSs coated with EPPS, TPPMS, and PEG-COOH were evaluated, showing a temperature increment of the colloidal solutions and optimal mitochondrial activity. We believe that this work contributes to understanding the phenomena and conditions that trigger changes in the morphology or stability of AuNSs and that AuNSs coated with TPPMS and PEG-COOH possess optimal properties for potential biomedical applications. [ABSTRACT FROM AUTHOR]

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]

We describe a competitive colorimetric assay that enables rapid and sensitive detection of galactose and reduced nicotinamide adenine dinucleotide (NADH) via colorimetric readouts and demonstrate its usefulness for monitoring NAD+-driven enzymatic reactions. We present a sensitive plasmonic sensing approach for assessing galactose concentration and the presence of NADH using galactose dehydrogenase-immobilized gold nanostars (AuNS-PVP-GalDH). The AuNS-PVP-GalDH assay remains turquoise blue in the absence of galactose and NADH; however, as galactose and NADH concentrations grow, the reaction well color changes to a characteristic red color in the presence of an alkaline environment and a metal ion catalyst (detection solution). As a result, when galactose is sensed in the presence of H2O2, the colored response of the AuNS-PVP-GalDH assay transforms from turquoise blue to light pink, and then to wine red in a concentration-dependent manner discernible to the human eye. This competitive AuNS-PVP-GalDH assay could be a viable analytical tool for rapid and convenient galactose quantification in resource-limited areas. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) peptides in the brain. Among the different forms of Aβ, oligomers (Aβo) are considered the most toxic and have been implicated in AD pathology. However, the accurate detection of Aβo remains challenging due to their low abundance and structural complexity. In this study, we propose an electrochemical sensing platform based on gold nanostars (AuS) for the detection of Aβo in AD. The AuS were functionalized with a peptide probe (PrPc) that specifically interacts with Aβo. The PrPc-AuS sensing platform exhibited high sensitivity and selectivity for Aβo detection. The electrochemical impedance spectroscopy (EIS) analysis showed significant changes in impedance upon binding of Aβo to the PrPc-AuS surface, providing quantitative information about the Aβo concentration. The platform demonstrated a linear detection range of 5–200 pM with a detection limit of 2 pM, meeting the requirements for clinical detection. This electrochemical sensing platform offers a promising approach for the early diagnosis and monitoring of AD, contributing to the development of point-of-care diagnostics for neurodegenerative diseases. [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]

Gold nanostars (AuNS) are anisotropic metal nanoparticles that display morphology-dependent optical properties. These include strong extinction coefficients in the near-infrared region of the spectrum and near-field enhancements. AuNS have been widely used for biomedical applications, including sensing, imaging, and photothermal therapy. To promote the use of AuNS for commercial (pre)-clinical purposes, the stability and shelf life need to be maximized. In pharmaceutics, lyophilization (also known as freeze-drying) is commonly employed to extend shelf life and facilitate logistics. However, lyophilization tends to induce stress on nanoparticles, causing irreversible aggregation. In this work, we studied the use of sucrose, glucose, sorbitol, poly-(vinylpyrrolidone) (PVP), and poly-(ethylene glycol) (PEG) as cryoprotectants during AuNS lyophilization, as well as their effect on particle shelf life, photothermal properties, and contrast agent performance. We explored three different AuNS that were obtained via one-pot synthesis with biocompatible 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS), 4-(2-hydroxyethyl) piperazine-1-ethanesulfonic acid (HEPES), and 3-(N-morpholino) propanesulfonic acid (MOPS) as the seedless synthetic protocol did not require cytotoxic surfactants that may complicate biological applications. As a reference, we used citrate-coated spherical gold nanoparticles (AuNPs). While AuNS synthesized with EPPS and HEPES could be lyophilized and resuspended in water in the absence of a cryoprotectant, the use of cryoprotectants (particularly sucrose) facilitated their reconstitution and improved shelf life. AuNPs and AuNS synthesized with MOPS irreversibly aggregated during lyophilization and required PVP for resuspension and long-term storage. The use of selected cryoprotectants preserved the photothermal characteristics and photoacoustic imaging signal generation of the nanoparticles after freeze-drying. Taken together, these findings provide insights into improving the stability and shelf life of nanoparticles, potentially contributing to the development of AuNS as biomedical products. [ABSTRACT FROM AUTHOR]

Gold nanostars with an average core diameter of 122,2 nm and a spike length of 114,6 nm were synthesized and characterized at a concentration of 5,36×1010 pcs/ml with an absorption maximum of 840 nm. Gold nanostars were coated with thiolated polyethylene glycol, its amount was about 8×104 molecules per 1 particle and about 4,4×1015 molecules/ml in the colloid. The zeta potential of gold nanostars coated with PEG-SH was −2.3 mV. The combined eff ect of gold nanostars and low-intensity infrared (808 nm) laser radiation on the bacteria Staphylococcus aureus 209 P and Escherichia coli 113-13 has been studied. Incubation of suspensions of microorganisms in the presence of nanoparticles without access to light did not lead to a signifi cant reduction in the number of bacteria. Irradiation for 30 min of bacterial suspensions containing nanoparticles caused the death of 39% of the S. aureus population and 80% of the E. coli population. During the thermometry of the studied suspensions, it was found that the temperature increase is dose-dependent. The increase in temperature of the control samples that did not contain photothermal agents did not exceed 1 °C in both cases throughout the entire time of the experiment. For suspensions of bacteria (equally S. aureus and E. coli) incubated with gold nanostars during irradiation, an increase in temperature indicators, on average, by 4 °C was revealed. The more pronounced antibacterial activity of the combination of gold nanostars and infrared (808 nm) laser radiation against E. coli can also be explained by the greater sensitivity of gram-negative microorganisms to photothermal exposure.

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]

Plasmonic colorimetric sensors have emerged as powerful analytical tools in biochemistry due to their localized surface plasmon resonance extinction in the visible range. Here, we describe the feasibility of NAD(P)/NAD(P)H as redox agents in enzymatic plasmonic gold nanostar (AuNS) assays for galactose quantification using three model enzymes, GalDH, AR and GalOx, immobilized separately on polyvinylpyrrolidone-capped AuNS scaffolds. These highly specific, sensitive and selective bioassays induce the transformation of AuNS into quasi-spherical nanoparticles during the biorecognition of galactose in water and synthetic blood matrices. As a result, using our inexpensive and simple AuNS plasmon bioassays, the presence of galactose may be detected spectrophotometrically and by the naked eye.

Abstract 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.

Surface-enhanced Raman spectroscopy (SERS), with high sensitivity to a broad range of molecules, can detect molecular "fingerprints" in a complex substance and thereby offers a promising solution for noninvasive medical diagnostics and personal healthcare monitoring. The eventual realization of such applications relies on SERS substrates with dense and uniform hot spots, good chemical stability, and high mechanical durability. With these criteria in mind, we developed a flexible nanoporous SERS substrate via the in situ synthesis of gold nanostars (AuNSs) on an ion-track-etched polycarbonate membrane. The nanoporous SERS substrate can realize analyte enrichment and exhibit excellent Raman performance by taking the advantage of hot spots on AuNSs. The SERS substrate yields highly repeatable and uniform signals for analytes (e.g., methylene blue) over a wide concentration range from 10–4 to 10–13 M. The flexible SERS substrate even can work well after 2000 times bending and exhibit excellent stability for long-term use. It can be prepared on a large scale with a low-cost and simple fabrication process and can be used repeatedly after cleaning to reduce the use-cost further. On-body experiments prove that the sweat SERS substrate allows effective identification of sweat contents, such as lactic acid and uric acid (UA), and the monitoring of diet-induced variation in sweat UA. The potential of the wearable nanoporous SERS substrates in sweat analysis thus has been demonstrated, opening possibilities for autonomous and noninvasive medical health monitoring. [ABSTRACT FROM AUTHOR]

Embedding Raman reporters within nanosized gaps of metallic nanoparticles is an attractive route for surface-enhanced Raman spectroscopy (SERS) applications, although often this involves complex synthesis procedures that limit their practical use. Herein, we present the tip-selective direct growth of silver satellites surrounding gold nanostars (AuNSt@AgSAT), mediated by a dithiol Raman reporter 1,4-benzenedithiol (BDT). We propose that BDT is embedded within nanogaps which form between the AuNSt tips and the satellites, and plays a key role in mediating the satellite growth. Not only proposing a rationale for the mechanistic growth of the AuNSt@AgSAT, we also demonstrate an example for its use for the detection of Hg2+ ions in water. The presence of Hg2+ resulted in amalgamation of the AuNSt@AgSAT, which altered both its structural morphology and Raman enhancement properties. This provides a basis for the detection where the Raman intensity of BDT is inversely proportional to the Hg2+ concentrations. As a result, Hg2+ could be detected at concentrations as low as 0.1 ppb. This paper not only provides important mechanistic insight into the tip-selective direct growth of the anisotropic nanostructure but also proposes its excellent Raman enhancement capability for bioimaging as well as biological and chemical sensing applications. [ABSTRACT FROM AUTHOR]

Bacterial infections have become a fatal threat because of the abuse of antibiotics in the world. Various gold (Au)-based nanostructures have been extensively explored as antibacterial agents to combat bacterial infections based on their remarkable chemical and physical characteristics. Many Au-based nanostructures have been designed and their antibacterial activities and mechanisms have been further examined and demonstrated. In this review, we collected and summarized current developments of antibacterial agents of Au-based nanostructures, including Au nanoparticles (AuNPs), Au nanoclusters (AuNCs), Au nanorods (AuNRs), Au nanobipyramids (AuNBPs), and Au nanostars (AuNSs) according to their shapes, sizes, and surface modifications. The rational designs and antibacterial mechanisms of these Au-based nanostructures are further discussed. With the developments of Au-based nanostructures as novel antibacterial agents, we also provide perspectives, challenges, and opportunities for future practical clinical applications. [ABSTRACT FROM AUTHOR]

In recent years, the disease burden of hyperuricemia has been increasing, especially in high-income countries and the economically developing world with a Western lifestyle. Abnormal levels of uric acid and hypoxanthine are associated with many diseases, and therefore, to demonstrate improved methods of uric acid and hypoxanthine detection, three different bodily fluids were analysed using surface-enhanced Raman spectroscopy (SERS) and high-performance liquid chromatography (HPLC). Gold nanostar suspensions were mixed with series dilutions of uric acid and hypoxanthine, 3 kDa centrifugally filtered human blood serum, urine and saliva. The results show that gold nanostars enable the quantitative detection of the concentration of uric acid and hypoxanthine in the range 5–50 μg/mL and 50–250 ng/mL, respectively. The peak areas of HPLC and maximum peak intensity of SERS have strongly correlated, notably with the peaks of uric acid and hypoxanthine at 1000 and 640 cm−1, respectively. The r2 is 0.975 and 0.959 for uric acid and hypoxanthine, respectively. Each of the three body fluids has a number of spectral features in common with uric acid and hypoxanthine. The large overlap of the spectral bands of the SERS of uric acid against three body fluids at spectra peaks were at 442, 712, 802, 1000, 1086, 1206, 1343, 1436 and 1560 cm−1. The features at 560, 640, 803, 1206, 1290 and 1620 cm−1 from hypoxanthine were common to serum, saliva and urine. There is no statistical difference between HPLC and SERS for determination of the concentration of uric acid and hypoxanthine (p > 0.05). For clinical applications, 3 kDa centrifugal filtration followed by SERS can be used for uric acid and hypoxanthine screening is, which can be used to reveal the subtle abnormalities enhancing the great potential of vibrational spectroscopy as an analytical tool. Our work supports the hypnosis that it is possible to obtain the specific concentration of uric acid and hypoxanthine by comparing the SER signals of serum, saliva and urine. In the future, the analysis of other biofluids can be employed to detect biomarkers for the diagnosis of systemic pathologies. [ABSTRACT FROM AUTHOR]

Gold nanostars (AuNSs) are synthesized using a seed-mediated growth method. The synthesized AuNSs solution is stable and shows a localized surface plasmon resonance (LSPR) band in the visible range, which is confirmed using ultraviolet–visible (UV–Vis) spectroscopy. Furthermore, the as-synthesized AuNSs were functionalized with melamine and used as a sensor for the colorimetric detection of uric acid (UA). The detection mechanism could be assessed through various analytical techniques such as UV–Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), zeta potential, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopic techniques. These methods exhibited a good linear regression between the absorption ratio of LSPR band of melamine–AuNSs and the concentration of UA (0–120 µM), with the detection limit of 8.50 nm. As a result, UA was quantitatively detected in biofluids by using melamine-AuNSs as a colorimetric sensor, revealing melamine–AuNSs–based colorimetric approach which could be used as a simple platform for UA assay in biofluids. Graphical Abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

Over the past few decades, colorimetric paper-based lateral flow immunoassay (LFIA) has emerged as a versatile analytical tool for rapid point-of-care detection of infectious diseases with high simplicity and flexibility. The LFIA sensitivity is based on color visualization of the antibody-labeled nanoparticles bound with the target analytes at the test line. Therefore, the nanoparticle design is crucial for LFIA sensitivity. The traditional LFIA is based on spherical gold nanoparticles, which usually suffer from poor sensitivity because of very low optical contrast at the test line. To improve the LFIA sensitivity, we have developed an LFIA based on gold nanostars (GNSs) with different branch lengths and sharpness (GNS-1, GNS-2, and GNS-3), which possess higher optical contrast than conventional gold nanospheres (GNSPs). We have selected the bacterium Yersinia pestis as a model analyte system. The effective affinity of GNSPs and GNSs with the Y. pestis fraction 1 (F1) protein was quantitively investigated by colorimetric and optical density measurements of the test line. The results show that GNS-3, which has maximum spike length and branch sharpness, exhibits the highest analytical sensitivity based on the limit of detection of the LFIA readout compared to other GNSs and GNSPs. The detection limit of the Y. pestis F1 antigen was achieved up to 0.1 ng/mL for GNS-3, which is 100 times lower than that for the GNSP at a 1 pmol/L concentration and 10 times lower than that for the reported procedure based on traditional gold nanoparticles. Overall, our prototype LFIA platform based on a highly spiked GNS (GNS-3) exhibits high analytical sensitivity, indicating it to be a promising candidate for routine LFIA application to detect infectious diseases. [ABSTRACT FROM AUTHOR]

The wide use and high toxicity of carbendazim (CBD) in agriculture pose unprecedented demands for convenient, sensitive, and cost-effective on-site monitoring. Herein, we propose a novel colorimetric and photothermal dual-mode lateral flow immunoassay (LFIA) based on plasmonic gold nanostars (AuNSs) for CBD detection in agricultural products. The AuNSs were synthesized via a rapid seed-mediated growth method (with growth time of ∼5 s). A stable immunoprobe was formed by adsorbing CBD antibodies onto AuNSs. This immunoprobe exhibited high conversion efficiency and sensitivity in photothermal detection with a low limit of detection (LOD) of 0.28 ng mL−1. The LOD of the colorimetric mode was higher (0.48 ng mL−1). The results of CBD detection in various agricultural products aligned well with ultra-performance liquid chromatography tandem mass spectrometry. Overall, our LFIA shows excellent sensitivity, specificity, reproducibility, and rapidness in CBD detection, and thus is a highly potential on-site platform in resource-limited environments. [Display omitted] • A colorimetric and photothermal lateral flow immunoassay was established. • Gold nanostars were used as both color labels and photothermal converters. • Gold nanostars were prepared by a convenient and fast seed-mediated growth method. • A low detection limit of 0.28 ng/mL for carbendazim was achieved. • Good performance for cabbage, citrus, and chives analysis was demonstrated. [ABSTRACT FROM AUTHOR]

A new synthesis strategy towards gold-coated silica nanoparticles is presented. The method provides an efficient, reliable and facile-coating process of well-defined star-shaped shell structures, characterized by UV-Vis, TEM, PXRD, DLS and zeta-potential measurements. A marked red shift of the Au-based plasmonic band to the region of the first biological window is observed offering great potential for future research of biological applications.

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]

A nanosensor comprising of gold nanostars (Au-Nstars)-graphitic carbon nitride (g-C3N4) nanocomposite layered on a glassy carbon electrode (GCE) to detect serotonin (ST) in various body fluids has been fabricated. The nanocomposite and the sensing platform have been thoroughly characterized with UV–visible spectroscopy (UV–vis), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray photoelectron spectroscopy (EDX), and electrochemical techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The designed ST detection probe has achieved a linear dynamic range (LDR) in the range 5 × 10−7 and 1 × 10−3 M with a limit of detection (LOD) of 15.1 nM (RSD < 3.3%). The ST detection capability of the fabricated sensor ranges between the normal and several abnormal pathophysiological situations. The sensor effectively detects ST in real matrices such as urine and blood serum, thus, showing its direct diagnostic applicability. Additionally, the sensor has been tested in the microenvironment of human embryonic kidney (HEK) cells to assess the possibility of ST secretion in cell lines. Interferences because of co-existing molecules have been evaluated, and the shelf-life of the fabricated sensor has been obtained as 8 weeks. [ABSTRACT FROM AUTHOR]

High quality visualization of live mammalian embryo is an important requirement for studying fetal development. Photoacoustic tomography (PAT) and optical coherence tomography (OCT) are two advanced imaging modalities that have been utilized for embryonic imaging separately. However, high contrast, multiscale, and deep tissue imaging of embryos in vivo remains challenging. Here, we demonstrate multimodal contrast-enhanced imaging of live embryos by gold nanostar-meditated near-infrared I (NIR-I) PAT and near-infrared II (NIR-II) OCT. We investigate intravenous and intravaginal administration of gold nanostars, and significant enhancement of signal, image contrast, and imaging depth are achieved for both PAT and OCT. Our findings may facilitate detailed studies of the morphological and functional changes during embryonic development. [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]

CRISPR/Cas 12a system based nucleic acid and non-nucleic acid targets detection faces two challenges including (1) multiple crRNAs are needed for multiple biomarkers detection and (2) insufficient sensitivity resulted from photobleaching of fluorescent dyes and the low kinetic cleavage rate for a traditional single-strand (ssDNA) reporter. To address these limitations, we developed a programmable DNA nanoswitch (NS)-regulated plasmonic CRISPR/Cas12a-gold nanostars (Au NSTs) reporter platform for detection of nucleic acid and non-nucleic acid biomarkers with the assistance of the spatial confinement effect. Through simply programming the target recognition sequence in NS, only one crRNA is required to detect both nucleic acid and non-nucleic acid biomarkers. The detection limit decreased by ∼196-fold for miRNA-375 and 122-fold for prostate-specific antigen (PSA), respectively. Moreover, versatile evaluation of miRNA-375 and PSA in clinical urine samples can also be achieved, according to which prostate cancer and healthy groups can be well identified.

We describe a competitive colorimetric assay that enables rapid and sensitive detection of galactose and reduced nicotinamide adenine dinucleotide (NADH) via colorimetric readouts and demonstrate its usefulness for monitoring NAD+-driven enzymatic reactions. We present a sensitive plasmonic sensing approach for assessing galactose concentration and the presence of NADH using galactose dehydrogenase-immobilized gold nanostars (AuNS-PVP-GalDH). The AuNS-PVP-GalDH assay remains turquoise blue in the absence of galactose and NADH; however, as galactose and NADH concentrations grow, the reaction well color changes to a characteristic red color in the presence of an alkaline environment and a metal ion catalyst (detection solution). As a result, when galactose is sensed in the presence of H2O2, the colored response of the AuNS-PVP-GalDH assay transforms from turquoise blue to light pink, and then to wine red in a concentration-dependent manner discernible to the human eye. This competitive AuNS-PVP-GalDH assay could be a viable analytical tool for rapid and convenient galactose quantification in resource-limited areas.

Surface-enhanced Raman scattering (SERS) is becoming widely used as an analytical tool, and the search for stable and highly responsive SERS substrates able to give ultralow detection of pollutants is a current challenge. In this paper we boosted the SERS response of Gold nanostars (GNS) demonstrating that their coating with a layer of silver having a proper thickness produces a 7-fold increase in SERS signals. Glass supported monolayers of these GNS@Ag were then prepared using simple alcoxyliane chemistry, yielding efficient and reproducible SERS chips, which were tested for the detection of molecules representative of different classes of pollutants. Among them, norfloxacin was detected down to 3 ppb, which is one of the lowest limits of detection obtained with this technique for the analyte. [ABSTRACT FROM AUTHOR]

Complex shapes of gold nanostars (GNS) have been the major obstacle to the comprehensive understanding of the rich plasmonic phenomena of GNS. We conducted extensive, systematic numerical study of far-field and near-field spectral responses of GNS for varying geometrical parameters (e.g., number of spikes, spike tip angle, and spike-to-core ratio) to elucidate the relationship between the optical property and the geometry of GNS. We found that symmetric configurations of GNS spikes generated both dipole and quadrupole localized surface plasmon (LSP) modes, their hybridization resulted in the final near-field intensity at the spike tips, and there existed a specific GNS geometry that optimized the hybridization and thus the E-field intensity for any given wavelength. From these results, we further identified the shapes of GNS that generated the strongest Surface Enhanced Raman Scattering (SERS) enhancement factors in the visible and NIR spectral range. Hence, our results provide guiding principles in determining the optimal geometry of GNS for SERS applications with any choice of excitation wavelength. [ABSTRACT FROM AUTHOR]

There has been increasing interest in evolution of plasmonic nanoplatforms based on noble metal nanoparticles to achieve ultrasensitive detection of trace analyte molecules through solution-based surface-enhanced Raman spectroscopy (SERS). This work presents a surfactant-free synthesis method of bimetallic gold nanostars coated with silver (BGNS-Ag) having sharp, high aspect-ratio spikes for achieving ultrahigh detection sensitivity and high reproducibility. Specifically, the unique BGNS-Ag platform combines both the strong SERS enhancement effects of gold nanostar sharp spikes and the high scattering feature of the silver–gold bimetallic structure. To achieve SERS reproducibility, this solution-based SERS measurement requires minimal sample preparation without addition of any external reagents, which can cause irregular aggregation of nanoparticles and reduce the reproducibility of SERS measurements. Moreover, we have streamlined our SERS sensing procedure by using standard well-plates and a portable Raman device for SERS measurements, which could be utilized for rapid on-site detection. This solution-based SERS performance was studied using methylene blue (MB) as a model analyte system. The detection limit of MB was as low as 42 pM, indicating high sensitivity of detection using BGNS-Ag. To illustrate the usefulness for environmental sensing, we showed that the SERS sensor can detect a pesticide, thiram, at a concentration as low as 0.8 nM. This study demonstrated that the BGNS-Ag system could serve as an effective and versatile plasmonic-active platform for reproducible, fast, and in-field detection of small organic analytes at trace levels. [ABSTRACT FROM AUTHOR]

Due to the body's systemic distribution of photothermal agents (PTAs), and to the imprecise exposure of lasers, photothermal therapy (PTT) is challenging to use in treating tumor sites selectively. Striving for PTT with high selectivity and precise treatment is nevertheless important, in order to raise the survival rate of cancer patients and lower the likelihood of adverse effects on other body sections. Here, we studied cold atmospheric plasma (CAP) as a supplementary procedure to enhance selectivity of PTT for cancer, using the classical photothermic agent's gold nanostars (AuNSs). In in vitro experiments, CAP decreases the effective power of PTT: the combination of PTT with CAP at lower power has similar cytotoxicity to that using higher power irradiation alone. In in vivo experiments, combination therapy can achieve rapid tumor suppression in the early stages of treatment and reduce side effects to surrounding normal tissues, compared to applying PTT alone. This research provides a strategy for the use of selective PTT for cancer, and promotes the clinical transformation of CAP. [ABSTRACT FROM AUTHOR]

A new synthesis strategy towards gold-coated silica nanoparticles is presented. The method provides an efficient, reliable and facile-coating process of well-defined star-shaped shell structures, characterized by UV-Vis, TEM, PXRD, DLS and zeta-potential measurements. A marked red shift of the Au-based plasmonic band to the region of the first biological window is observed offering great potential for future research of biological applications. [ABSTRACT FROM AUTHOR]