Quo Vadis, Nanoparticle-Enabled In Vivo Fluorescence Imaging?

Abstract

The exciting advancements that we are currently witnessing in terms of novel materials and synthesis approaches are leading to the development of colloidal nanoparticles (NPs) with increasingly greater tunable properties. We have now reached a point where it is possible to synthesize colloidal NPs with functionalities tailored to specific societal demands. The impact of this new wave of colloidal NPs has been especially important in the field of biomedicine. In that vein, luminescent NPs with improved brightness and near-infrared working capabilities have turned out to be optimal optical probes that are capable of fast and high-resolution in vivo imaging. However, luminescent NPs have thus far only reached a limited portion of their potential. Although we believe that the best is yet to come, the future might not be as bright as some of us think (and have hoped!). In particular, translation of NP-based fluorescence imaging from preclinical studies to clinics is not straightforward. In this Perspective, we provide a critical assessment and highlight promising research avenues based on the latest advances in the fields of luminescent NPs and imaging technologies. The disillusioned outlook we proffer herein might sound pessimistic at first, but we consider it necessary to avoid pursuing “pipe dreams” and redirect the efforts toward achievableyet ambitiousgoals.

Beyond the Energy Gap Law: The Influence of Selection Rules and Host Compound Effects on Nonradiative Transition Rates in Boltzmann Thermometers

“…Remote temperature sensing with noninvasive optical methods becomes increasingly popular. [ 1–4 ] Potential application areas range from biothermal imaging, [ 5,6 ] temperature monitoring in catalysis, [ 7–10 ] microelectronics, [ 11 ] or molecular logics [ 12 ] to the investigation of fundamental thermodynamic phenomena [ 13 ] at the micro‐ and nanoscale. One of the conceptually simplest ways of optical temperature sensing, also in terms of the required setup, is the exploitation of the luminescence intensity ratio (LIR) of two emission bands due to radiative transitions from two thermally coupled excited levels of an ensemble of non‐interacting ions.…”

Uptake of Upconverting Nanoparticles by Breast Cancer Cells: Surface Coating versus the Protein Corona

“… 5 − 7 Furthermore, for NPs to be effectively translated to the clinic, fundamental studies of their photochemical properties must be complimented with research on their biological behavior and cytotoxicity. 3 , 7 − 10 …”

“…These nanomaterials differ in size, shape, composition, and function; thus, rationally engineered NPs act as probes for biosensing, optical imaging, therapy, and nanoscale thermometry, to name a few. − In the context of in vitro / in vivo use of NPs, successful NP entry into the cell and accumulation of NPs at the targeted site becomes vital. It is imperative to have knowledge of the NP behavior in a biological environment, interaction with cells, as well as the fate of the NPs once inside the cell. − Furthermore, for NPs to be effectively translated to the clinic, fundamental studies of their photochemical properties must be complimented with research on their biological behavior and cytotoxicity. ,− …”

Less is more: dimensionality reduction as a general strategy for more precise luminescence thermometry

“…Such conditions are particularly relevant for biomedical applications where, to avoid damage, the excitation power density needs to stay below specific safety levels. Moreover, photon extinction by biological tissues strongly reduces both the number of excitation photons reaching the luminescent probe (nanoparticle) and the number of emitted photons collected by the detection systems 41 . Swieten et al have demonstrated that when working in conditions of low signal-to-noise ratio, the thermal uncertainty is affected and the performance of the thermometer is compromised 42 .…”