Fluorescence switch plays a vital role in bioelectronics and bioimaging. Herein, we presented a new kind of facile electrostatic complex nanoparticles (ECNs) for fluorescence switching in cells and marking of individual cell. The ECNs were prepared by mixing positively charged poly(6-(2-(thiophen-3-yl)ethoxy) hexyl trimethylammonium bromide) (PT) and negatively charged diarylethene sodium salt (DAE-COONa). DAE-COONa is a photoswitchable molecule which can be transformed between the ring-closed form and ring-open form under the irradiation of UV or visible light. The closed-form of DAE-COONa can efficiently quench the fluorescence of PT through intermolecular energy transfer, while the open form of DAE-COONa does not influence the emission of PT. Thus, the fluorescence of ECNs can be modulated by light irradiation, and the ECNs with good fluorescence switching performance have been employed for fluorescence imaging and individual cell lighting up process successfully. We demonstrate that the electrostatic complex strategy provides a facile method to construct fluorescence switch for selective cell marking and imaging applications.