In recent years, quantum dots (QDs) have emerged as bright, color-tunable light sources for various applications such as light-emitting devices, lasing, and bioimaging. One important next step to advance their applicability is to reduce particle-to-particle variations of the emission properties as well as fluctuations of a single QD’s emission spectrum, also known as spectral diffusion (SD). Characterizing SD is typically inefficient as it requires time-consuming measurements at the single-particle level. Here, however, we demonstrate multiparticle spectroscopy (MPS) as a high-throughput method to acquire statistically relevant information about both fluctuations at the single-particle level and variations at the level of a synthesis batch. In MPS, we simultaneously measure emission spectra of many (20-100) QDs with a high time resolution. We obtain statistics on single-particle emission line broadening for a batch of traditional CdSe-based core-shell QDs and a batch of the less toxic InP-based core-shell QDs. The CdSe-based QDs show significantly narrower homogeneous line widths, less SD, and less inhomogeneous broadening than the InP-based QDs. The time scales of SD are longer in the InP-based QDs than in the CdSe-based QDs. Based on the distributions and correlations in single-particle properties, we discuss the possible origins of line-width broadening of the two types of QDs. Our experiments pave the way to large-scale, high-throughput characterization of single-QD emission properties and will ultimately contribute to facilitating rational design of future QD structures.

Circular dichroism (CD) spectroscopy is a powerful optical technique for the study of chiral materials and molecules. It gives access to an enantioselective signal based on the differential absorption of right and left circularly polarized light, usually obtained through polarization analysis of the light transmitted through a sample of interest. CD is routinely used to determine the secondary structure of proteins and their conformational state. However, CD signals are weak, limiting the use of this powerful technique to ensembles of many molecules. Here, we experimentally realize the concept of photothermal circular dichroism, a technique that combines the enantioselective signal from circular dichroism with the high sensitivity of photothermal microscopy, achieving a superior signal-to-noise ratio to detect chiral nano-objects. As a proof of principle, we studied the chiral response of single plasmonic nanostructures with CD in the visible range, demonstrating a signal-to-noise ratio better than 40 with only 30 ms integration time for these nanostructures. The high signal-to-noise ratio allows us to quantify the CD signal for individual nanoparticles. We show that we can distinguish relative absorption differences for right circularly and left circularly polarized light as small as g_min = 4 × 10^-3 for a 30 ms integration time with our current experimental settings. The enhanced sensitivity of our technique extends CD studies to individual nano-objects and opens CD spectroscopy to numbers of molecules much lower than those in conventional experiments.