Multiphotonic Ablation and Electro-Capacitive Effects Exhibited by Candida albicans Biofilms

Abstract

This work reports the modification in the homogeneity of ablation effects with the assistance of nonlinear optical phenomena exhibited by C. albicans ATCC 10231, forming a biofilm. Equivalent optical energies with different levels of intensity were irradiated in comparative samples, and significant changes were observed. Nanosecond pulses provided by an Nd:YAG laser system at a 532 nm wavelength in a single-beam experiment were employed to explore the photodamage and the nonlinear optical transmittance. A nonlinear optical absorption coefficient -2 × 10^-6 cm/W was measured in the samples studied. It is reported that multiphotonic interactions can promote more symmetric optical damage derived by faster changes in the evolution of fractional photoenergy transference. The electrochemical response of the sample was studied to further investigate the electronic dynamics dependent on electrical frequency, and an electro-capacitive behavior in the sample was identified. Fractional differential calculations were proposed to describe the thermal transport induced by nanosecond pulses in the fungi media. These results highlight the nonlinear optical effects to be considered as a base for developing photothermally activated phototechnology and high-precision photodamage in biological systems.

Keywords: Candida albicans; Nd:YAG laser; electrical capacitance; nonlinear optical absorption; optical ablation; optical absorbance.

Figure 1

(a) Schematic illustration of the laser ablation experiment. (b) Representative photo of the experimental setup.

Figure 2

(a) Brightfield microscopy of C. albicans in vitro biofilm; (b) fungal cell wall α-D-mannosyl residues labeled with Concanavalin A stain, observed by epifluorescence microscopy; (c) biofilm architecture observed by scanning electron microscopy. In all cases, in vitro biofilm was started with an inoculum of 1 × 10⁶ blastoconidia/mL and was incubated at 37 °C for 24 h.

Figure 3

(a) Impedance vs. electrical frequency of C. albicans with 1 kHz to 100 kHz and 10 mV (b). Absorbance spectra of C. albicans ATCC 10231 in vitro biofilm starting with an inoculum of 1 × 10⁶ blastoconidia/mL and incubating at 37 °C for 24 h.

Figure 4

(a) Experimental results of optical ablation effect in C. albicans obtained by a single shot of a high-irradiance optical pulse. (b) Experimental results of optical ablation in C. albicans by a sequence of low-irradiance pulses. (c) Numerical results obtained by the Fractional Newton Cooling Law for ablation in the nonlinear optical effect. (d) Numerical results obtained by the Fractional Newton Cooling Law for ablation in the linear optical effect.

Figure 5

Numerical simulations estimated using FCL to describe a laser ablation process induced by (a) nonlinear optical effect with 1 pulse at 5 MW/cm². (b) Nonlinear optical effect by 1 pulse at 7.5 MW/cm². (c) Nonlinear optical effect by 1 pulse at 10 MW/cm². (d) Nonlinear optical effect by 1 pulse at 12.5 MW/cm². (e) Linear optical effect by 5 pulses at 1.25 MW/cm². (f) Linear optical effect by 5 pulses at 1.875 MW/cm². (g) Linear optical effect by 5 pulses at 2.5 MW/cm². (h) Linear optical effect by 5 pulses at 3.125 MW/cm².

Figure 6

(a) Demonstration of the propagation of heat in C. albicans ATCC 10231 when the sample is exposed to an optical ablation. (b) Numerical simulation with $\alpha$ as the fractional order as 0.87, and dotted lines have $\alpha$ as 1 for temperature changes determined by C. albicans ATCC 10231 under normalized temperature vs. time.

Figure 7

Transmitted irradiance vs. incident irradiance in C. albicans.