.Sensitive detection of weak acoustic signals at nanometer scale is challenging. Here, the authors present an acoustic detection system based on a single molecule as a probe, where frequency and... Show more.Sensitive detection of weak acoustic signals at nanometer scale is challenging. Here, the authors present an acoustic detection system based on a single molecule as a probe, where frequency and amplitude of acoustic vibrations can be extracted from its minute variations in distance to the surface of a plasmonic gold nanorod.Sensitive detection of local acoustic vibrations at the nanometer scale has promising potential applications involving miniaturized devices in many areas, such as geological exploration, military reconnaissance, and ultrasound imaging. However, sensitive detection of weak acoustic signals with high spatial resolution at room temperature has become a major challenge. Here, we report a nanometer-scale system for acoustic detection with a single molecule as a probe based on minute variations of its distance to the surface of a plasmonic gold nanorod. This system can extract the frequency and amplitude of acoustic vibrations with experimental and theoretical sensitivities of 10 pm Hz(-1/2) and 10 fm Hz(-1/2), respectively. This approach provides a strategy for the optical detection of acoustic waves based on molecular spectroscopy without electromagnetic interference. Moreover, such a small nano-acoustic detector with 40-nm size can be employed to monitor acoustic vibrations or read out the quantum states of nanomechanical devices. Show less
We demonstrate two-photon-excited single-mole-culefluorescence enhancement by single end-to-end self-assembledgold nanorod dimers. We employed biotinylated streptavidin asthe molecular linker,... Show moreWe demonstrate two-photon-excited single-mole-culefluorescence enhancement by single end-to-end self-assembledgold nanorod dimers. We employed biotinylated streptavidin asthe molecular linker, which connected two gold nanorods in end-to-end fashion. The typical size of streptavidin of around 5 nmseparates the gold nanorods with gaps suitable for the access offresh dyes in aqueous solution, yet small enough to give very hightwo-photonfluorescence enhancement. Simulations show thatenhancements of more than 7 orders of magnitude can be achievedfor two-photon-excitedfluorescence in the plasmonic hot spots.With such high enhancements, we successfully detect two-photon-excitedfluorescence for a common organic dye (ATTO 610) at the single-molecule, single-nanoparticle level Show less
End-to-end gold nanorod dimers provide unique plasmonic hotspots with extremely large near-field enhancements in the gaps. Thereby they are beneficial in a wide range of applications, such as... Show moreEnd-to-end gold nanorod dimers provide unique plasmonic hotspots with extremely large near-field enhancements in the gaps. Thereby they are beneficial in a wide range of applications, such as enhancing the emissions from ultra-weak emitters. For practical purposes, synthesis of gold nanorod dimers with high yield, especially on the substrates, is essential. Here, we demonstrate two controllable strategies to synthesize gold nanorod dimers based on the self-assembly of gold nanorods, either in bulk solution or on the surface of a glass substrate directly. Both methods can give a high yield of gold nanorod dimers, yet, assembling them directly on the substrate provides more flexibility in controlling the shape and size of each nanorod within the dimer. We also show that these gold nanorod dimers can be used to enhance two-photon-excited fluorescence signals at the single-molecule level. Show less
