Plasmonic colloidal nanoparticles with open eccentric cavities via acid-induced chemical transformation

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been considered a promising technique for the detection of trace molecules in biomedicine and environmental monitoring. The ideal metal nanoparticles for SERS must not only fulfill important requirements such as high near-field enhancement and a tunable far-field response but also overcome the diffusion limitation at extremely lower concentrations of a target material. Here, we introduce a novel method to produce gold nanoparticles with open eccentric cavities by selectively adapting the structure of non-plasmonic nanoparticles via acid-mediated surface replacement. Copper oxide nanoparticles with open eccentric cavities are first prepared using a microwave-irradiation-assisted surfactant-free hydrothermal reaction and are then transformed into gold nanoparticles by an acidic gold precursor while maintaining their original structure. Because of the strong near-field enhancement occurring at the mouth of the open cavities and the very rough surfaces resulting from the uniformly covered hyperbranched sharp multi-tips and the free access of SERS molecules inside of the nanoparticles without diffusion limitation, adenine, one of the four bases in DNA, in an extremely diluted aqueous solution (1.0 pM) was successfully detected with excellent reproducibility upon laser excitation with a 785-nm wavelength. The gold nanoparticles with open eccentric cavities provide a powerful platform for the detection of ultra-trace analytes in an aqueous solution within near-infrared wavelengths, which is essential for highly sensitive, reliable and direct in vivo analysis. INTRODUCTIONThere is a strong demand for trace-molecule detection techniques that are simple, rapid, highly sensitive and reproducible, spanning from diagnostics in medicine to the detection of base sequence mutation. Surface-enhanced Raman spectroscopy (SERS) could be a promising candidate for extremely sensitive molecular finger-printing techniques that fulfill these technological and detection system criteria. 1 SERS is a near-field phenomenon that relies on the intensified electric fields (E-fields) on a metal nanostructure when its localized surface plasmon resonance is excited by light. 2 These enhanced E-fields lead to a large enhancement of the Raman scattering signal. 3 Although the hot spots exhibiting these intensively localized E-fields that are usually expected between two (or multiple) noble metal nanoparticles and the sharp nanoscale tips can amplify Raman signals by 410 6 times for trace molecule detection, 4,5 they are not easily obtained. 6,7 Several attempts have been made to increase the sensitivity and reproducibility for active SERS substrates. Two-dimensional arrays of various SERS-active substrates were introduced 8,9 but were not suitable for detection in solution or in an in vivo system because of

One-step fabrication of hollow-channel gold nanoflowers with excellent catalytic performance and large single-particle SERS activity

“…8,9 However, the majority of the existing hollow nanostructures (e.g., hollow nanospheres, nanocages and nanoshells) have closed outer shells, which reduce the accessible surface and limits the diffusivity of guest molecules into/out of the cavity. 10 In contrast, the presence of an open internal cavity has been demonstrated to provide a large accessible surface area, enhanced up-take capacity for guest molecules and highly effective diffusivity, all of which are beneficial for drug delivery, 11 catalytic [12][13][14] and SERS 15 capabilities of hollow nanostructures.…”

Thermal Sensitivity on Eccentric Gold Hollow Nanoparticles: A Perspective from Atomistic Simulations

“…Understanding the limits of stability on hollow nanospheres is a crucial aspect for the performance of hollow structures, moreover considering that the introduction of irregular surfaces has been used as a route to control the catalytic activity, plasmonic, and sensing , on this kind of nanostructures. − While catalysis or plasmonic are especially sensitive to the eccentricity parameters, the experimental conditions would lead to thermal effects that could reduce eccentric nanosphere performance. Our work is aligned with these findings and tries to understand the collapse modes and the limits of eccentricity for reliable applications of eccentric hGNP.…”