Silica-coated gold nanorods are core–shell nanostructures consisting of a gold nanorod core encased in a layer of silica (SiO₂). The silica shell can be deposited as a dense solid layer or a mesoporous layer with tunable pore structure. Shell thickness can be precisely controlled—typically ranging from a few nanometers to over 30 nm.
Silica vs. Mesoporous Silica
It's worth distinguishing between dense silica and mesoporous silica coatings. Dense silica provides excellent protection and stability but offers limited space for cargo loading. Mesoporous silica (mSiO₂), with pores between 2 and 50 nm, creates a high-surface-area reservoir for drugs, photosensitizers, or Raman reporters—enabling multifunctional theranostic platforms.
Synthesis of Silica-Coated Gold Nanorods
Silica‑coated gold nanorods (AuNR@SiO₂) are synthesized through a two‑step process: first, gold nanorods with aspect ratios of 2:1–10:1 and diameters of 5–50 nm are produced via the seed‑mediated growth method using CTAB as a structure‑directing surfactant; second, a silica shell is deposited onto the nanorods via a sol–gel process with tetraethyl orthosilicate (TEOS), where the adsorbed CTAB molecules act as a template. The shell thickness (ranging from 0.5 nm to over 30 nm) is precisely controlled by adjusting TEOS concentration, reaction time, and surfactant levels. Recent advances also enable anisotropic coating—selectively depositing silica on the tips or sides of the rods—which significantly enhances SERS sensitivity by concentrating analytes at the tips where the electromagnetic field is strongest, opening new avenues for chemical sensing and diagnostics.
Biomedical Applications
Photothermal Therapy
Silica-coated gold nanorods are highly effective photothermal agents. The gold core efficiently converts NIR light into localized heat, while the silica shell protects against aggregation and degradation.
A recent study demonstrated that Au@SiO₂-HA-DOX nanoparticles—gold nanorods coated with silica shells and functionalized with hyaluronic acid for tumor targeting—exhibited excellent photothermal stability and sustained temperature elevation under NIR irradiation. In a mouse breast cancer model, NIR-assisted therapy significantly inhibited tumor growth while maintaining stable body weight and good biocompatibility.
Drug Delivery
Mesoporous silica-coated gold nanorods are ideal drug delivery vehicles. The mesoporous structure provides high surface area for drug loading, while the gold core enables NIR-triggered drug release.
The Au@SiO₂-HA-DOX system achieved a doxorubicin (DOX) loading efficiency of 65.9% with sustained release characteristics. The nanoparticles exhibited selective targeting and stronger cytotoxicity towards cancer cells, with cellular uptake 1.7 times higher than free DOX and an IC₅₀ value of 1.36 µM (compared to 2.01 µM for free DOX). This nanohybrid system represents a promising strategy for improving chemotherapy efficacy while reducing toxicity.
Bioimaging
The AuNR core provides contrast for multiple imaging modalities:
Photoacoustic imaging: Strong NIR absorption generates photoacoustic signals for deep-tissue imaging
Dark-field optical imaging: Gold nanorods exhibit strong light scattering
Surface-enhanced Raman spectroscopy (SERS): Silica-coated AuNRs serve as powerful SERS substrates
SERS Biosensing
Mesoporous silica-coated gold nanorods act as a colloidally stable Raman sensing platform with a built-in analyte size cutoff—allowing small molecules to enter the pores while excluding larger interferents.
Anisotropic silica coating on the tips of gold nanorods has been shown to boost SERS sensitivity, enabling detection of cationic dyes at lower concentrations than uniform silica coatings. These SERS-active particles can be used for multiplex and ultrasensitive detection of biomolecules.
Theranostic Platforms
Silica-coated gold nanorods are increasingly being developed as theranostic platforms that integrate therapy and diagnostics. The silica shell not only stabilizes the nanoparticles but also provides extra space for cargo loading, making them multifunctional in cancer theranostics.
Beyond Biomedicine
The utility of silica-coated gold nanorods extends beyond biomedicine to areas such as catalysis, environmental monitoring, and energy storage. Their unique optical and electronic properties, combined with the stability provided by the silica shell, make them promising platforms for a wide range of applications.
How to Buy?
BOT Bioparticles specializes in producing high-quality Silica-coated Gold Nanorods with uniform particle size and excellent chemical stability.
Key advantages of BOT Bioparticles' Silica-coated Gold Nanorods include:
l Uniform particle size
l Surface modifiable
l Good chemical stability
l High surface electric field enhancement effect
l Strong optical absorption capacity
l High photothermal conversion efficiency
BOT Bioparticles offers professional custom synthesis and surface functionalization services to meet specific application requirements—including silica coating with tailored shell thicknesses and surface modifications.