What to choose: Gold Nanostars or Gold Nanourchins?

Typically consist of a central core with a limited number of relatively long, high‑aspect‑ratio spikes, giving well‑defined sharp tips.                                                                                              

Have a spherical core densely covered with many shorter protrusions, creating a highly rough, “sea‑urchin‑like” or “raspberry-like” surface with many moderate‑curvature tips.

Offer fine tunability of their localized surface plasmon resonance (LSPR) from visible to NIR‑I/NIR‑II simply by adjusting spike length, number, and core size, allowing precise matching to specific laser wavelengths for imaging or therapy.                                                                                                                                                                

LSPR is also red‑shifted relative to smooth spheres due to surface roughness and protrusions, and can reach NIR‑I, but tuning is typically coarser and leads to broader bands. This broad response is useful for wide‑band illumination but less ideal when very narrow spectral matching is needed.                  

Strong, highly localized electric fields concentrate at the spike tips and in gaps between spikes, leading to very high field enhancements. Simulations and experiments show enhancement factors high enough to detect very low analyte concentrations (down to ~10⁻¹²–10⁻¹³ M for optimized SERS nanotags).

The dense, rough surface produces numerous hot spots over the entire particle, but individual hot spots are typically less intense than at the sharpest nanostar tips. This yields strong average enhancement across large areas, beneficial for ensemble measurements and solid‑substrate sensors.

Depending on size, nanostars can be tuned to be strongly absorbing (for photothermal therapy) or strongly scattering (for imaging), with fine control via spike morphology.

Nanourchins typically show strong extinction with a significant scattering component over a broad spectral range, useful for colorimetric and LSPR‑shift‑based biosensing.

Nanostars are often reported as among the highest‑performing SERS substrates, with enhancement factors exceeding those of spheres, rods, and many other anisotropic shapes because of their sharp spikes. Reviews highlight nanostars as “prime candidates” for SERS due to their adjustable plasmon resonance and intense, tip‑localized hot spots.                                                                           

Nanourchins also provide strong SERS signals thanks to their extremely rough, multi‑tip surfaces, with enhancements suitable for ultrasensitive detection, although reported EF values are typically somewhat lower or more heterogeneous than optimized nanostars. Their advantage lies in dense hot‑spot coverage rather than maximum single‑spot intensity.

Nanostars‑based SERS nanotags have been engineered for multiplexed detection of biomolecules (e.g., DNA, proteins) in complex media, with detection limits in the low picomolar range using NIR lasers.                                              

Nanourchins‑like gold structures have been used as SERS‑active layers in microfluidic chips and lateral‑flow assays, enabling label‑free detection of analytes via signal enhancement across large sensing areas.

Spike length and density allow precise tuning of the main plasmon band to match specific therapeutic wavelengths, maximizing light absorption in NIR‑I and NIR‑II for PTT. For example, “armored” nanostars designed for 808 and 1064 nm show strong, stable extinction at these wavelengths for combined PTT and photoacoustic imaging.

Nanourchins can also be tuned into NIR‑I through control of growth conditions and roughness, but the response is broader and less sharply peaked, which can reduce peak absorption cross‑section compared with a carefully tuned nanostar.                                                                                                               

High absorption cross‑section and strong field confinement at spikes translate into efficient photothermal conversion, often yielding rapid local temperature rises under moderate NIR power densities. Reviews emphasize that nanostars are particularly effective PTT agents because their shape maximizes local electron density and light–heat conversion in NIR.                                                                                

Rough nanourchins surfaces also enhance light–heat conversion, but quantitative comparisons suggest that, at matched volumes and wavelengths, spike‑optimized nanostars can deliver higher localized heating per particle. Nanourchins, however, provide more uniform heating over larger assemblies, beneficial for bulk tissue or surface treatments.                  

Well‑engineered nanostars with protective shells (e.g., silica, polymer, or “armored” coatings) show improved resistance to reshaping and melting, maintaining their photothermal efficiency over repeated irradiation cycles.                                                                               

Nanourchins are also reasonably stable, but high local heating at many small tips can lead to some smoothing at very high powers; the inherently rough morphology means that even partially reshaped particles often retain usable photothermal and SERS activity.

Strong LSPR and SERS responses enable highly sensitive detection of nucleic acids, proteins, and small molecules, often in sandwich assays or as encoded SERS nanotags for multiplexed detection. For instance, nanostar‑based SERS tags have been used to detect biomarkers at sub‑pM levels in complex biological fluids.                            

Nanourchins are excellent for label‑free and colorimetric sensing, where binding‑induced refractive‑index changes or aggregation cause visible spectral shifts and SERS enhancement.Their broad LSPR makes them suitable for simple, naked‑eye readouts in point‑of‑care tests and paper‑based sensors.

Cellular uptake and bio-compatibility

Nanostars synthesized with biocompatible coatings (PEG, proteins, silica) show low cytotoxicity and good cellular uptake, enabling intracellular SERS imaging and photothermal therapy. Reviews describe their use in theranostics platforms combining imaging, SERS readout, and PTT in cancer models.                                                                                                                                                       

Nanourchins also exhibit good biocompatibility when properly coated, and their rough surface can increase protein adsorption and cell interaction, which may enhance uptake but also requires careful control to avoid nonspecific binding. They have been explored for in vitro biosensing and imaging where broad plasmon bands are advantageous.                          

Nanostars have been used in advanced PTT systems, including real‑time photoacoustic thermometry and imaging, where precisely tuned NIR absorption and high photothermal conversion yield efficient tumor ablation in preclinical models. Their sharp spikes also enable combined SERS guidance and PTT for image‑guided therapy.                                                                                

Nanourchins have been investigated for PTT and photoacoustic imaging as well, benefiting from their rough surfaces and high extinction; they provide robust heating and signal generation, though with somewhat less control over exact resonance position. Their strength is in robust, multimodal contrast over a wide spectral range.

- SERS‑encoded nanostar tags for multiplex food contaminant detection and biosensing, achieving very low detection limits. 

- “Armored” nanostars integrated with real‑time photoacoustic monitoring for precision photothermal cancer therapy.                                                                                                  

- Nanourchins‑based plasmonic sensors for detecting biomolecules via LSPR shifts and SERS in microfluidic or paper‑based devices. 

- Rough gold nanourchins films for surface‑based SERS detection of environmental or clinical analytes with simple optical setups.

For applications requiring highly tunable, narrow NIR resonances and combined SERS–PTT–imaging (e.g., cancer theranostics with controlled wavelength selection), nanostars are often favored because their spike geometry is more easily engineered and optimized.                                                                                                        

For applications focused on low‑cost, robust sensing platforms (e.g., paper‑based SERS, broad‑band colorimetric/LSPR sensors) where large‑area roughness and broad optical response are assets, nanourchins are frequently selected due to their dense protrusions and strong ensemble signals.