Design and characterization of optical nanorulers of single nanoparticles using optical microscopy and spectroscopy

Current conventional imaging methods cannot determine sizes of single nanoparticles (NPs) in solution and living organisms at the nanometre scale, which limits the applications of NPs. In this study, we developed new imaging calibration approaches to characterize the sizes of single Ag NPs in solution at nanometre resolution by measuring their size-dependent scattering localized-surface-plasmon-resonance (LSPR) spectra and scattering intensity using dark-field optical microscopy and spectroscopy (DFOMS). We synthesized nearly spherical shape Ag NPs, ranging from 2 to 110 nm in diameter, and characterized the sizes of single NPs using high-resolution transmission electron microscopy, and the LSPR spectra and scattering intensity of single NPs using DFOMS. We constructed calibration curves of the peak wavelength (lambda(max)) of LSPR spectra or scattering intensity of single NPs versus their sizes. These calibration curves allow us to determine the sizes of single NPs at 1 nm resolution by measuring the LSPR spectra or scattering intensity of single NPs using DFOMS. These new approaches enable us to create optical nanorulers (calibration curves) of single Ag NPs for simultaneously imaging and measuring sizes of multiple single NPs in solution in real time at nanometre resolution using optical microscopy. One can now use these new imaging calibration approaches to study and characterize single NPs in solution and living organisms in real time for a wide variety of applications.