Faculty Members

CHEUNG, Nai Ho - Professor
張迺豪

 

B.A.(Hons.), Chicago; M.Sc.,
Ph.D., Cornell University

 

 
 
 
 

 

Contact: Rm. T905
Tel: (852) 3411-7034
Email: nhcheung@hkbu.edu.hk
Website: Laser Analytics Group

    We are interested in the physics of laser-material interactions, especially that of laser-induced processes for analytical and biomedical applications. Our aim is to develop novel optical solutions for ultra-trace analysis and bio-molecular studies. Two current activities are described below.

     

  1. Analytical spectroscopy of laser plumes
    When a sample target is ablated by a laser pulse, the vapor plume can be analyzed spectroscopically for composition determination. We pioneered two optical techniques for plume analysis that can detect trace amounts of multi elements simultaneously. One is by means of resonance-enhanced plasma spectroscopy. It minimizes the continuum background associated with laser induced plasmas. Relative to laser-induced breakdown spectroscopy, the signal-to-noise ratio is improved by orders of magnitude, thus allowing the quantitation of sodium and potassium at the single blood cell level. The other technique utilizes laser-excited atomic fluorescence. It has been traditionally handicapped by its one wavelength–one transition specificity. We showed, however, that numerous elements could be induced to fluoresce at a single excitation wavelength of 193 nm provided that the analytes were imbedded in dense plumes, such as those produced by pulsed laser ablation. This method eliminates the continuum plasma background and sub-ppb sensitivity was demonstrated in the analysis of aqueous lead colloids.

     

  2. Bio-molecule imaging
    In total internal reflection, the evanescent wave induces fluorophores at the interface to emit while those in the bulk solution remain dark. It therefore singles out interface events. We use the technique to study the nonspecific adsorption of proteins at interfaces, at the ensemble as well as single molecule levels. Heterogeneities among pure protein species and protein-protein interactions were revealed with unprecedented details. We also investigate the chain of biochemical reactions starting with the specific binding of surface-immobilized protein receptors with their hormone ligands. We aim at elucidating the very rich kinetics of agonistic versus antagonistic bindings, down to single molecule resolution.

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