Luminescent nanomaterials have shown promise for thermal sensing in bio-applications, yet little is known of the role of organic coatings such as supported lipid bilayers on the thermal conductivity between the nanomaterial and its environment. Additionally, since the supported lipid bilayer mimics the cell membrane, its thermal properties are fundamentally important to understand the spatial variations of temperature and heat transfer across membranes. Herein we describe a new approach that enables direct measurement of these thermal properties using a LiYF4:Er 3+ /Yb 3+ upconverting nanoparticle encapsulated within a conformal supported lipid bilayer and dispersed in water as a temperature probe yielding the temperature gradient across the bilayer. The thermal conductivity of lipid bilayer was measured as function of the temperature, being 0.20±0.02 W·m -1 ·K -1 at 300 K. For the uncapped nanoparticles dispersed in water, the temperature dependence of the thermal conductivity was also measured in the 300-314 K range as [0.63-0.69]±0.11 W·m -1 ·K -1 . Using a lumped elements model, we calculate the directional heat transfer at each of the system interfaces, namely nanoparticle-bilayer and bilayer-nanofluid, opening a new avenue to understand the membrane biophysical properties as well as the thermal properties of organic and polymer coatings.

The upconversion quantum yield (ΦUC) is an essential parameter for the characterization of the optical performance of lanthanoid-doped upconverting nanoparticles (UCNPs). Despite its nonlinear dependence on excitation power density (Pexc), it is typically reported only as a single number. Here, we present the first measurement of absolute upconversion quantum yields of the individual emission bands of blue light-emitting LiYF4:Yb3+,Tm3+ UCNPs in toluene. Reporting the quantum yields for the individual emission bands is required for assessing the usability of UCNPs in various applications that require upconverted light of different wavelengths, such as bioimaging, photocatalysis and phototherapy. Here, the reliability of the ΦUC measurements is demonstrated by studying the same batch of UCNPs in three different research groups. The results show that whereas the total upconversion quantum yield of these UCNPs is quite high-typically 0.02 at a power density of 5 W cm-2-most of the upconverted photon flux is emitted in the 794 nm upconversion band, while the blue emission band at 480 nm is very weak, with a much lower quantum yield of ∼6 × 10-5 at 5 W cm-2. Overall, although the total upconversion quantum yield of LiYF4:Yb3+,Tm3+ UCNPs seems satisfying, notably for NIR bioimaging, blue-light demanding phototherapy applications will require better-performing UCNPs with higher blue light upconversion quantum yields.

Lanthanide‐doped upconverting nanoparticles (UCNPs) convert low energy near‐infrared (NIR) absorbed light to ultraviolet, visible, and NIR emissions. For biological applications, water dispersibility, bio‐compatibility, and high colloidal stability must be achieved. Enveloping nanoparticles with supported lipid bilayer (SLB) is an alternative method to solve this problem. Here, the formation and characterization of a SLB on LiYF4:Tm3+/Yb3+ UCNPs is shown.

Soft matter shells for nanoparticles provide an alternative approach to the more traditional inorganic core–shell nanoconstructs. In the latter, functionality and biocompatibility often require the addition of a hydrophilic organic coating. Herein, a supported lipid bilayer serves as a soft matter shell that has the physicochemical properties that enable a dynamic system capable of providing biocompatibility, encapsulation, and release of small molecule active agents. Direct coupling of the conformal, supported lipid bilayer containing an azobenzene-derivatized lipid with an upconversion nanoparticle provides the means to photocontrol the bilayer properties, generating a multifunctional coating. The close contact of the bilayer with the nanoparticle surface eliminates problems associated with Brownian motion for the energy transfer; the mechanism of energy transfer was determined to be dominated by radiative reabsorption using time-resolved photoluminescence. Release of an encapsulated dye, as a hydrophobic drug model, was achieved with significantly lower proportions of azobenzene-derivatized lipid than has been reported for UV-triggered release from liposomes. This work highlights the potential of the described nanoconstruct for light controlled delivery applications, especially in a biological context and in vivo applications, for which NIR excitation is of paramount importance for low toxicity and deeper tissue penetration.

To circumvent the need for direct UV excitation in a supramolecular hydrogel composed of an azobenzene-modified poly(acrylic acid) copolymer and deoxycholate-β-cyclodextrin as a crosslinker, we modified this system for use with LiYF4:Tm3+/Yb3+ upconverting nanoparticles, which emit UV light upon NIR excitation. A complete gel-sol transition was observed in 60 minutes upon 980 nm irradiation. No change was observed under similar conditions of a control sample over the same period of time.

An understanding of the cellular uptake and trafficking of nanoparticles is important for the design of efficient nanoparticle-based nanomedicines. Herein we compare the uptake and cytotoxicity of diamond-shape, lanthanide upconverting nanoparticles (LiYF 4 :Tm 3+ /Yb 3+ UCNPs) with different surface properties. Coating the UCNP with a supported lipid bilayer yielded negligible cytotoxicity on A549 human lung cancer cells, albeit with a lower, but still significant, UCNP uptake compared to oleatecapped and oleate-free UCNPs. Using inhibition studies and cellular imaging we demonstrate that the UCNPs are internalized by endocytosis and energy independent pathways and trafficked to the endoplasmic reticulum, Golgi apparatus, and lamellar and lipid bodies. Upon incorporation of a photostimulus within the bilayer coating, release of a Nile red as a hydrophobic drug model was demonstrated.

Heat transfer and thermal properties at the nanoscale can be challenging to obtain experimentally. These are potentially relevant for understanding thermoregulation in cells. Experimental data from the transient heating regime...

Supported lipid bilayers mimic cell membranes and may be an alternative method to produce water dispersible nanoparticles with high biocompatibility and provide the possibility of drug encapsulation inside the lipid bilayer. On page 865, J. A. Capobianco and co‐workers apply this approach to lanthanide‐doped upconverting nanoparticles that convert low energy light (NIR) to UV and visible.