Gold nanoparticle synthesis coupled to fluorescence turn-on for sensitive detection of formaldehyde using formaldehyde dehydrogenase

Abstract

Ultrasensitive detection of toxins by nanoparticle–fluorophore interaction has been studied extensively in the past decade. The present study highlights the detection of formaldehyde based on fluorescence turn-on induced by NADH mediated GNP synthesis. The growth solution consisted of CTAB, Au³⁺ and fluorescein dye. Extensive fluorescence quenching was observed upon interaction of fluorescein with the growth solution. However, addition of NADH led to dose dependent fluorescence turn-on. This behavior was successfully employed for the ultrasensitive detection of formaldehyde (0.01 pg to 300 pg mL⁻¹ with R² = 0.9439) as a function of NADH using formaldehyde dehydrogenase enzyme. Metal ion interactions with the proposed system were also studied. We propose that the initial fluorescence quenching is due to CTAB–fluorescein–Au³⁺ interaction. Addition of NADH to the growth solution led to initiation of gold nanoparticle synthesis by the reduction of Au³⁺ to Au⁰ that induced more polarity on the CTAB micellar surface causing fluorescein–CTAB transition and turn-on fluorescence, further leading to the detection of NADH. Also, at increased NADH/formaldehyde concentration, a fluorescence decrease was observed which is due to the efficient synthesis of gold nanoparticles leading to spectral overlap. The proposed method of Au³⁺ reduction coupled to fluorescence turn-on can be applied for monitoring NADH dependent dehydrogenase reactions at ultrasensitive levels.