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

Ultrasensitive detection of toxins by nanoparticle-fluorophore interaction
has been studied extensively in the past decade. 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 a dose dependent fluorescence turn-on. This behavior was successfully
employed for ultrasensitive detection of formaldehyde (0.01pg - 300pg/mL 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 detection of NADH. Also, at increased
NADH/formaldehyde concentration, fluorescence decrease was observed which
is due to efficient synthesis of gold nanoparticle 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.