What are Gold Nanostars’ “hot spots”, and why do they matter?
Gold Nanostars' "hot spots" are tiny regions at the sharp tips of their spiky branches and in very small gaps between spikes, where electromagnetic fields intensify dramatically due to localized surface plasmon resonance (LSPR), amplifying signals in techniques like surface-enhanced Raman spectroscopy (SERS) by factors up to millions (Hrelescu et al., 2011, Becerril-Castro et al., 2022, Mousavi et al., 2020). These hotspots arise when light excites the free electrons in the gold nanostructure, causing them to oscillate and create ultra-strong local electric fields, especially at the pointed ends where electron density curves sharply. This makes nanostars superior to spherical nanoparticles for sensing, as the spikes concentrate energy like lightning rods focus electrical discharge.
Hotspots in gold nanostars are tunable by adjusting spike length, number, and overall size, shifting their plasmonic response from visible to near-infrared wavelengths for targeted applications. Aggregates or core-satellite designs (nanostars linked to other gold particles) multiply hotspots between particles, boosting SERS even further (Shiohara et al., 2015).
SERS‑based chemical and biological sensing
One of the most important application areas of gold nanostars hot spots is SERS‑based chemical and biological sensing. Analytical studies show that nanostars‑based SERS substrates can detect trace analytes, such as environmental contaminants or small biomolecules, at ultra‑low concentrations because the molecules located in the hot spots experience a huge enhancement of their Raman signal. Recent reviews on gold nanostructures for SERS highlight nanostars as particularly attractive because they combine strong, tip‑localized hot spots with good colloidal stability and synthetic tunability, making them suitable for reproducible substrates in routine analytical chemistry (López-Lorente, 2021, Becerril-Castro et al., 2022).
Bioimaging
The most direct use of nanostars hot spots is as surface‑enhanced Raman scattering (SERS) “nanotags” for bioimaging (Andreiuk et al., 2022). Here, Raman reporter molecules are anchored in the hot‑spot regions (tips and inter‑spike gaps), and the nanostars are further functionalized with antibodies, aptamers, or peptides to target specific receptors or tumor markers. SERS with gold nanostars images cancer biomarkers like EpCAM on cell surfaces, quantifying expression in breast (MCF-7) and prostate (PC-3) cancer cells at sub nanomolar levels using aptamer-functionalized hotspots (Bhamidipati et al., 2018). Super-resolution SERS tracks peptide-labeled nanostars binding integrin receptors (αvβ3) on cell membranes, revealing nanoscale interactions and localizing individual particles through their intense hot‑spot SERS signatures (de Albuquerque and Schultz, 2020).
In vivo Raman imaging and theranostics
Because nanostars also convert light to heat efficiently at their hot spots, many designs integrate photothermal therapy with SERS imaging (“image‑guided theranostics”), using the same particles for pre‑treatment tumor mapping and subsequent localized ablation (Tian et al., 2025). Liu et al. (2015) developed a gold nanostars probe enabling surface-enhanced Raman scattering for in vivo tumor detection through intact skin, alongside x-ray computed tomography and two-photon luminescence imaging in sarcoma mouse models. In vivo NIR laser photothermal therapy under maximum permissible exposure ablated tumors containing gold nanostars, confirming theranostics potential.
Photoacoustic imaging with nanostar hot spots
Gold nanostars are strong photoacoustic (PA) contrast agents because their branched shape and hot spots boost optical absorption in the NIR, which is then converted into ultrasonic waves. PA imaging with nanostars has been used to visualize structures such as sentinel lymph nodes and tumors with signals severalfold higher than surrounding blood, benefiting from the intense absorption at tip hot spots (Kim et al., 2011).
Real‑time intracellular tracking and “smart” probes
Gold nanostars have also been integrated into real‑time tracking systems in living cells, where hot‑spot SERS signals report on drug release or microenvironment changes. For instance, nanostars–drug conjugates have been followed inside single cells, using SERS from molecules located in the hot spots to distinguish bound vs released drug states during transferring (Minati et al., 2021).
Li et al. (2021) described Au nanostars probes enabling "turn-on" fluorescence and "turn-off" SERS via plasmon quenching, ideal for single-chip detection of ions/biomarkers with complementary readouts.
Multifunctional probes and Lab‑on‑Chip devices
Beyond pure sensing and imaging, gold nanostars with engineered hot spots are being integrated into multifunctional platforms. Their unique optical properties make possible dual‑mode sensing (like combining SERS and fluorescence) in compact diagnostic devices, helping integrate multiple tests onto a single microchip platform. One approach combines a gold nanostar core (providing hot spots and photothermal conversion) with an insulating shell and fluorescent or quantum dot components to create hybrid probes that support both SERS and fluorescence or luminescence readout. An example is a gold nanostar@SiO₂@CdSe/ZnS structure, where the nanostar core generates hot spots for SERS and efficient light absorption, while the outer semiconductor shell provides an additional optical channel, enabling dual‑mode detection in complex media. Such architectures are promising for lab‑on‑chip devices, where small volumes, multiplexed detection, and strong signals are required for rapid diagnostics (Shan et al., 2018).
Folks et al. (2025) highlighted nanostars' superior hotspots (>100x SERS gain vs. spheres) in thermally responsive nanogels for microfluidic SERS, with preserved optical tunability supporting fluorescence integration for reusable lab-on-chip multiplexing.
Thus, gold nanostars drive advances in real-time sensing inside cells, targeted photothermal immunotherapy, and lab-on-chip diagnostic devices. Their flexible structures and stability in body-like conditions make them ideal next-generation agents for combined therapy and diagnostics (theranostics).
References
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