Step-wise Multi-photon Excitation of Melanin and Graphite

Research Overview

Melanin is the characteristic chromophore of human skin with various potential biological functions, which include protection from solar radiation, antioxidant defense, and camouflage. Melanin is also involved in skin diseases such as malignant melanoma, an aggressive skin cancer with high metastatic potential. Despite its importance, melanin is poorly understood because it is an insoluble polymer without well-defined structure, which is difficult to isolate and study. Our previous research has shown that it is possible to generate three-photon fluorescence in melanin with near infrared light. In three-photon fluorescence, an electron absorbs three photons and then emits one photon as fluorescence. In most cases, simultaneous absorption is required, which involves using of an expensive ultra-short pulsed laser. Our research has shown that step-wise procedure occurs in melanin. An electron at ground state absorbs one photon and is excited to the first state. Then the second photon is absorbed by the electron and excites the electron to the second state. A fluorescence photon is emitted when the electron is excited to the third state (excited state) by the third photon. This process can be generated each by using continuous wave (CW) laser, which is relatively low cost. Our research focuses on understanding the step-wise multi-photon fluorescence in melanin and pursues possible application in clinic use.

Optical Science Laboratory

This research project is part of the work at the Optical Science Laboratory of Chuck DiMarzio in the Department of Electrical and Computer Engineering at Northeastern University. For other projects see Optical Science Lab Research Page.

  • Zhenhua Lai, Josef Kerimo, Charles A. DiMarzio, "Melanin fluorescence spectra by step-wise three photon excitation", Photonics West, Feb 2012 Proc. Vol. 8227
  • Kerimo, J., Rajadhyaksha, M., & DiMarzio, C.A., "Enhanced Melanin Fluorescence by Stepwise Three-photon Excitation", Photochem. & Photobio., 2011, 87: 1042-1049.

Last update 11 June 2012