We have developed a new approach in which we harness the advantages of UCNPs and AuNRs for cancer treatment and produce a single nanoplatform (see Figure 1).26 We take advantage of the powerful diagnostic and thermal sensing capacities of UCNPs (see Figure 2), as well as the known therapeutic properties of AuNRs. By coupling the AuNRs and UCNPs together, we are able to increase the upconverted emission brightness and enhance their diagnostic strength.
Molecules or fluorophorescent emitters that are attached to, or near to, an AuNR surface will experience an emission enhancement. This is caused by the strong surface plasmon resonance (SPR) on the surface of the AuNRs. In particular, the enhancement can be created by tuning the gold SPRs so that they are closer to the excitation of the ytterbium/erbium-doped (Yb3+/Er3+) core.27 In our experiments, we have observed an emission enhancement of our nanodevice, which is caused by the AuNR coupling (see Figure 3). This enhancement is produced by the localized SPR of the AuNR at about 980nm, which is resonant with the absorption of the Yb3+/Er3+ ions in the doped core. Our results clearly show an equal enhancement of the green (540nm) and red (650nm) emissions (i.e., a three- to four-fold increase in emission intensity).
We have also conducted time-resolved studies to investigate the enhancement effect of our nanodevices. In our preliminary work, we have studied the influence of AuNR coupling on the time-resolved decay of the upconversion emissive states. Our data (see Figure 4) shows a stronger dependence for green emission than for red emission on the AuNR coupling. We observe no change in the rise time for the decay of either the green or red emissions. This indicates that there is very little absorption enhancement at near-IR wavelengths.
To achieve effective photothermal treatments—so that protein destruction occurs—the temperature of the heated regions must rise to at least 40–45°C.24, 28 With the nanothermometer property of our UCNPs, we are also able to quantify the local temperature of the coupled photothermally excited AuNRs. We can thus determine the laser fluence and time duration that is needed to generate the required temperature for killing the appropriate cancer cells. Combined with the 3D thermal sensing property of the UCNPs, our approach can potentially ensure that cancer lesions are completely destroyed.
We have developed and experimentally tested new nanodevices that can be used for effective photothermal cancer treatments. In our devices, we couple upconverting nanoparticles and gold nanorods. As such, we can achieve brighter emissions, as well as improved diagnostic and thermal sensing capabilities compared with conventional photothermal treatment approaches. In our upcoming work, we will map the transport of photothermal excitation between two separate UCNP-AuNR particles that are embedded within a tissue phantom. We will also map the 3D temperature profile that leads to tissue-wide cell damage.
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