Abstract
Although thermal conductivity gas analyzers are ubiquitous in industry, shrinking the sensing unit to a microscopic scale is rarely achieved. Since heat transfer between a metal nanoparticle and its ambient gas changes the temperature, refractive index, and density of the gaseous surrounding, one may tackle the problem using a single nanoparticle’s photothermal effect. Upon heating by a 532 nm laser, a single gold nanoparticle transfers heat to the surrounding gas environment, which results in a change in the photothermal polarization of a 633 nm probe laser. The amplitude of the photothermal signal correlates directly with the concentration of binary gas mixture. In He/Ar, He/N2, He/air, and H2/Ar binary gas mixtures, the signal is linearly proportional to the He and H2 molar concentrations up to about 10%. The photothermal response comes from the microscopic gaseous environment of a single gold nanoparticle, extending from the nanoparticle roughly to the length of the gas molecule’s mean free path. This study points to a way of sensing binary gas composition in a microscopic volume using a single metal nanoparticle.
Highlights
Gas sensors are becoming ubiquitous in our lives, with applications in the chemical industry, household safety, environmental protection, and border security, just to name a few
A new family of optical gas sensoring based on the localized surface plasmon resonance (LSPR) of metal nanoparticles has started to attract attention.[7−9] Using metal nanoparticles for sensing is a good approach to sensor miniaturization.[10−12] Intrinsically, many metal nanoparticles exhibit environment-dependent LSPR,[13−15] which reveals the physical and chemical changes of the environment and shows how a nanoparticle interacts with its microscopic surroundings
The photothermal gas sensing imaging signals are sensitive to single protein binding events on metal nanoparticles.[32]
Summary
Gas sensors are becoming ubiquitous in our lives, with applications in the chemical industry, household safety, environmental protection, and border security, just to name a few. Langhammer and co-workers[16] demonstrated hydrogen sensing by LSPR spectroscopy using Pd nanodisks as a sensing platform They showed that the adsorption and desorption of hydrogen on Pd nanoparticles could be measured accurately.[17] Different types of Pd nanoparticles have since been studied for hydrogen sensing such as Pd nanorings,[18] Pd nanocubes,[19] and nanoscale Pd sandwich structures.[20] In addition, a Pd nanoparticle could couple with a gold antenna to enhance its hydrogen sensitivity by concentrating an electric field in the coupling region.[21] Gas sensing based on Ag nanoparticles was demonstrated, by measuring the disappearance and reappearance of the LSPR peaks upon exposure to oxygen and hydrogen, respectively, after surface redox reactions.[22]. The relatively good SNR was due to a large number of metal
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