Photophysical lock-in detection enables background-free upconversion emission imaging
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This folder contains all raw data underlying the results presented in a manuscript, submitted to Nano Letters, and entitled: Photophysical lock-in detection enables background-free upconversion emission imaging Authored by: Niusha Bagheria, Chenyi Wangb, Du Guoa, Anbharasi Lakshmanana, Qi Zhua, Xu Chena, Nahid Ghazyanic, Qiuqiang Zhanb, Georgios A. Sotirioud, Haichun Liu*a, Jerker Widengren*a a Experimental Biomolecular Physics, Department of Applied Physics, KTH Royal Institute of Technology, SE-106 91, Stockholm, Sweden b Centre for Optical and Electromagnetic Research, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, P. R. China c Faculty of Physics, Kharazmi University, Tehran, Iran. d Department of Microbiology Tumor and Cell Biology Karolinska Institute, SE-171 77, Stockholm, Sweden Corresponding authors: *haichun@kth.se, jwideng@kth.se The data files containing raw data and results of the analysis are grouped according to the different figures in the manuscript where the extracted results are presented. ABSTRACT Lanthanide-based upconversion nanoparticles (UCNPs) have attracted considerable attention in biomedical applications, due to their anti-Stokes shifted emission enabling autofluorescence-free signal detection. However, residual excitation light can still interfere with their relatively low brightness. While commonly used lock-in detection can distinguish weak signals from substantial random background, concurrently modulated residual excitation light is not eliminated. This remains a challenge, particularly under demanding experimental conditions. Here, we propose a photophysical lock-in detection (PP-LID) approach based on the discovery that UCNPs can act as frequency mixers in response to intensity-modulated excitation. Particularly, modulated excitation with more than one base modulation frequency can generate additional low-frequency beating-signals. These signals are resolvable by frame-rate-limited cameras, devoid of ambient and residual excitation light, and can be regulated through nanoparticle engineering. Extracting beating-signals by PP-LID thus provides a strategy to significantly enhance signal-to-background conditions in UCNP-based bioimaging and biosensing. Keywords: Upconversion nanoparticles (UCNPs), nonlinearity, modulation, lock-in detection, second harmonic, beating frequency, fast Fourier Transform (FFT)
