On the possibility of high-precision photothermal microeffects and the measurement of fast thermal denaturation of proteins

The precision of laser-induced effects is often limited by thermal and ther momechanical collateral damage. Adjusting the pulsewidth of the laser to th e size of the absorbing structure can at least avoid thermal side effects a nd facilitates a selective treatment of vessels or pigmented cells. Further extending the precision of thermal effects below cellular dimensions by us ing nanometer sized particles could open up new fields of applications for lasers in medicine and biology. Calculations show that under irradiation wi th nano- or picosecond laser pulses gold particles of submicrometer size ca n easily be heated by several hundred K, High temperatures have to be used for subcellular thermal effects, because heat confinement to such small str uctures requires the thermal damage to occur in extremely short times. Esti mating the denaturation temperature by extrapolating the Arrhenius equation from a time range of minutes and seconds into a time range of nano- and pi coseconds leads to temperatures beta;een 370 K-470 K, There is evidence tha t in aqueous media, due to the surface tension, these temperatures can be g enerated at the surface of nanometer sized particles without vaporization o f the surrounding water, In order to show whether or not an extrapolation of the damage rates over s ix to nine orders of magnitude gives correct data, a temperature-jump exper iment was designed and tested which allows to measure denaturation rates of proteins in the millisecond time range. Denaturation of chymotrypsin was o bserved within 300 mu s at temperatures below 380 K, The rate constants for the unfolding of chymotrypsin followed the Arrhenius equation up to rates of 3000 s(-1).