Lanthanide upconversion nonlinearity: a key probe feature for background-free deep-tissue imaging

This folder contains all raw data underlying the results presented in a manuscript, submitted to Nano Letters, and entitled:

Lanthanide upconversion nonlinearity: a key probe feature for background-free deep-tissue imaging

Authored by:

Niusha Bagheria, Chenyi Wangb, Du Guoa, Anbharasi Lakshmanana, Qi Zhua, 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:

*[e-mail], [e-mail]

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 imaging and biosensing applications, largely 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, with excitation light modulation and phase-sensitive 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.

In this work, we explore the inherent nonlinear response of UCNP emission and discover that UCNPs can act as frequency mixers in response to intensity-modulated excitation. Thereby, frequency components in the UCNP emission can be distinguished, not present in the excitation and background. Moreover, by modulated excitation with more than one base modulation frequency additional low-frequency beating-signals can be generated. By detecting these signals both random ambient light and residual excitation light can be effectively eliminated, and they also have the important advantage to be resolved, by low-speed detectors, such as cameras. Through nanoparticle engineering we show how these beating-signals can be significantly enhanced and detected in tissue with minimized background levels, providing 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)