Photophysical lock-in detection enables background-free upconversion emission imaging

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 imagingAuthored by:Niusha Bagheria, Chenyi Wangb, Du Guoa, Anbharasi Lakshmanana, Qi Zhua, Xu Chena, Nahid Ghazyanic, Qiuqiang Zhanb, Georgios A. Sotirioud, Haichun Liua, Jerker Widengrena a Experimental Biomolecular Physics, Department of Applied Physics, KTH Royal Institute of Technology, SE-106 91, Stockholm, Swedenb Centre for Optical and Electromagnetic Research, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, P. R. Chinac Faculty of Physics, Kharazmi University, Tehran, Iran.d Department of Microbiology Tumor and Cell Biology Karolinska Institute, SE-171 77, Stockholm, SwedenCorresponding authors:*[email protected], [email protected] 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.ABSTRACTLanthanide-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)