Physical mechanism of delayed luminescence from human serum

The fluorescence spectra, delayed luminescence (DL) spectra and DL decay dynamics of human serum were studied by fluorescence and time resolved emission spectrum technology under different excitation conditions in this paper. The results we obtained are shown as follows: (1) the DL spectrum is similar to the time resolved fluorescence spectrum within 50ns after Ps laser pulse excitation. (2) The intensity and decay time of DL from the serum samples are dependent on excitation power and irradiation time. Under fixed excitation power, the longer irradiation time is, the higher the DL intensity; after the excitation energy reaches about 200mJ, the DL intensity is nearly unchanged. The change of DL decay time follows the similar regulation to that of DL intensity. (3) As the excitation energy increases, the spectral distribution of the relative intensities exhibits an observable change. The higher the excitation energy is, the stronger the relative intensity at short wavelength region. The results show that the delayed luminescence of human serum is mainly originated from its delayed fluorescence, phosphorescence, and induced bio-photon emission. These results may be also useful for the development of serum diagnosis technology.