Improved molecular fingerprint analysis employing multi-branched gold nanoparticles in conjunction with surface-enhanced Raman scattering

Gold Nanoraspberries for Surface-Enhanced Raman Scattering: Synthesis, Optimization, and Characterization

In this work, we demonstrate the synthesis of gold nanoraspberries (AuNRB) using a HEPES buffer at room temperature. The study aimed to identify and compare the physicochemical conditions of the AuNRB and gold nanospheres (AuNS) of similar size to a selected set of reporter molecules. The dispersion stability of shape-controlled and AuNS of similar diameters was investigated in three different physiological media, ultrapure water, phosphate-buffered saline (PBS), and fetal bovine serum (FBS), and compared to understand the effect of NP shape, dispersion stability, and surface-enhanced Raman scattering (SERS) enhancement. We have used two nonresonant reporters, trans-1,2-bis(4-pyridyl) ethylene (BPE) and biphenyl-4-thiol (BPT), and a resonant reporter, IR820 (also known as new indocyanine green), a clinically approved dye for diagnostic studies, to explore the relative benefit of using molecular electronic resonance, i.e., comparing SERS vs surface-enhanced resonance Raman scattering (SERRS) with these nanoparticles. SERS has been explored extensively for biomedical applications, but the synthesis of bright gold nanoparticles and the appropriate Raman label is still challenging. To understand and optimize the SERS process, we have characterized both types of gold nanoparticles, ranging from their average size, ζ-potential, and ultraviolet-visible (UV-vis) absorption. It has been found that AuNRB and AuNS are most stable when dispersed in ultrapure water, while significant aggregation of both types has been observed when dispersed in PBS. With 10% FBS, there was a slight shift and increase in the surface plasmon absorbance peak, which resulted from an increase in particle size due to protein corona formation around the gold nanoparticles. For SERS efficiency, it has been found that AuNRB outperform AuNS with all reporters. Further, the resonant reporter, IR820, has provided a higher SERS signal compared to BPE and BPT and with its FDA approval for clinical use is clearly a strong candidate for future in vivo application.

Near-infrared light-triggered theranostics for tumor-specific enhanced multimodal imaging and photothermal therapy

The major challenge in current clinic contrast agents (CAs) and chemotherapy is the poor tumor selectivity and response. Based on the self-quench property of IR820 at high concentrations, and different contrast effect ability of Gd-DOTA between inner and outer of liposome, we developed "bomb-like" light-triggered CAs (LTCAs) for enhanced CT/MRI/FI multimodal imaging, which can improve the signal-to-noise ratio of tumor tissue specifically. IR820, Iohexol and Gd-chelates were firstly encapsulated into the thermal-sensitive nanocarrier with a high concentration. This will result in protection and fluorescence quenching. Then, the release of CAs was triggered by near-infrared (NIR) light laser irradiation, which will lead to fluorescence and MRI activation and enable imaging of inflammation. In vitro and in vivo experiments demonstrated that LTCAs with 808 nm laser irradiation have shorter T1 relaxation time in MRI and stronger intensity in FI compared to those without irradiation. Additionally, due to the high photothermal conversion efficiency of IR820, the injection of LTCAs was demonstrated to completely inhibit C6 tumor growth in nude mice up to 17 days after NIR laser irradiation. The results indicate that the LTCAs can serve as a promising platform for NIR-activated multimodal imaging and photothermal therapy.

Ligand Controlled Morphology Evolution of Active Intermediates for the Syntheses of Gold Nanostars

Gold nanostars have unique plasmonic properties that are related to the highly branched nanostructures. However, it is challenging to precisely control these branches. Here we studied the reaction kinetics on the seed-mediated growth process of gold nanostars using in situ UV-vis spectroscopy. The impact of hydroquinone ligands on the formation and evolution of active intermediates was systematically explored. In addition, we improved the classical seed-mediated method to achieve a much better control on the final morphology of gold nanostars by a sudden addition of a high concentration ligand solution. Our method can significantly advance the syntheses of gold nanostars and provide numerous opportunities to prepare nanomaterials with unique morphology and plasmonic properties.