Fig. 3 In vitro magnetothermal induction of
Ca2+ influx in TRPV1-expressing 293T cells. (a, b)
Fold changes in fluorescence intensity
(Ft/F0 values) of Fluo-4 in 293T cells
during magnetothermal treatment with anti-His-FVIOs at Fe concentrations
ranging from 51 to 498 μg/mL, and with anti-His-SPIOs at Fe
concentrations of 498, 816, and 1095 μg/mL. AMF conditions: H = 20 mT
and f = 290 kHz. (c) SIM images of TRPV1-expressing cortical
neurons (red) bound to anti-His-FVIO-FL (green). (d) Fold changes in
fluorescence intensity (Ft/F0 values) of
Fluo-4 as a function of time for TRPV1-expressing cortical neurons
treated with FVIOs (324 μg/mL) or SPIOs (1095 μg/mL). AMF conditions: H
= 20 mT and f = 290 kHz. The data are presented as the mean ±
SEM; the solid lines indicate the means, and the shaded areas indicate
the SEMs.
We further examined Ca2+ influx in cultured
TRPV1-expressing cortical neurons using the nanoheaters anti-His-FVIOs. FL-labeled anti-His-FVIOs successfully targeted TRPV1
on cortical neurons (Figure 3c). Moreover, the cells were
loaded with Fluo-4 to monitor Ca2+ influx (Figure S10,
movie S2, Supporting Information). As shown in Fig. 3d, upon
magnetothermal stimulation with anti-His-FVIOs at an Fe concentration
of 324 μg/mL, Ca2+ fluorescence in cortical
neurons rapidly increased from 50 to 200 s. In contrast, the
Ca2+ fluorescence intensity in neurons increased
slowly in response to magnetothermal stimulation by the anti-His-SPIOs
at an Fe concentration of 1095 μg/mL. Therefore, the anti-His-FVIO
nanoheater is believed to enable efficient magnetothermal neural
activation at low Fe concentrations.