Gold nanoparticles (AuNPs) are attractive photothermal agents for cancer therapy because they show efficient local heating upon excitation of surface plasmon oscillations. The strong absorption, efficient heat conversion, high photostability, inherent low toxicity and well-defined surface chemistry of AuNPs contribute to the growing interest in their photothermal therapy (PTT) applications. The facile tunability of gold nanostructures enables engineering of AuNPs for superior near-infrared photothermal efficacy and target selectivity, which guarantee efficient and deep tissue-penetrating PTT with mitigated concerns regarding side effects by nonspecific distributions. This article discusses the current research findings with representative near-infrared-active AuNPs, which include nanoshell, nanorod, nanocage, nanostar, nanopopcorn and nanoparticle assembly systems. AuNPs successfully demonstrate potential for use in PTT, but several hurdles to clinical applications remain, including long-term toxicity and a need for sophisticated control over biodistribution and clearance. Future research directions are discussed, especially regarding the clinical translation of AuNP photosensitizers.

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Nearly monodisperse colloidal superstructures of cadmium chalcogenide quantum dots (QDs) are reported. The superstructures, which we named as supra quantum dot (SQD), are typically composed of hundreds of a-few-nanometer-sized QDs three-dimensionally (3D) assembled by oriented attachment. The synthesis route for SQD is quite universal and can be extended to CdS, CdSe, CdTe, and CdSeTe alloy. The size of SQD can be tuned from tens of nanometers to over a hundred nanometers. In the case of CdSe SQD, zinc-blende seeds (primary QDs) act as the building block for the formation of the 3D assembled structures, SQDs, with discrete intermediates nanostructures. Primary seeds, 4 nm tetrahedral shaped QDs, assembled into a large tetrahedron of 20 nm. The 20 nm tetrahedrons, in turn, self-assembled into a larger tetrahedron of 40 nm. The discrete-in-size and sequential assemblies were followed by conventional growth from the remaining precursors and ripening within the particles to result in spheroidal SQDs. SQDs allow surface ligand exchange without losing the structural integrity. Size-selective precipitation of SQDs can provide monodisperse SQDs that can assemble into ordered superlattices. The size and composition tunability of SQDs and their capability to form superlattices can provide a new solution-processable building block for superstructure with programmable physical and chemical properties.

This study explored the size dependence of colloidal CdSe nanocrystals (NCs) on the photovoltaic properties of CdSe NC/poly(3hexylthiophene) (P3HT) hybrid bulk-heterojunction (BHJ) solar cell devices. The size-dependent photovoltaic performance was achieved by utilizing CdSe supraquantum dots (SQDs), which are three-dimensionally interconnected colloidal superstructures composed of hundreds of CdSe quantum dots (QDs). The average size of the SQDs can span tens of nanometers, which allow the formation of percolation networks in BHJ films. The open-circuit voltage of the devices was observed to be proportional to the size of the SQDs because of their ideal percolation networks. The photocurrents were determined by the competition between the charge separation and charge transport abilities controlled by the SQD sizes. Overall, the 46 nm-sized CdSe SQD-device demonstrated the highest power conversion efficiency (PCE) of 0.95%, which was 3.2 times higher than that of the control 4.3 nm-sized CdSe QD device. However, further increasing the SQD size resulted in a decrease in the PCE because of the inherent carrier recombination loss within the SQDs. To overcome this "Goldilocks problem," we tuned the energy level at the surface region of the CdSe SQDs via electron-donating 4-methylthiophenol (MTP) ligand exchange. The MTP-treated CdSe SQDs further improved the device performance by enhancing the charge separation and increasing the energy level offset at the CdSe SQD/P3HT interface.

Incorporation of transition metal dopants within a semiconductor nanocrystal has a tremendous effect on the optical and magnetic properties of the semiconductor nanocrystals. Herein, we report on a novel synthesis of second near‐infrared‐emitting photoluminescent Mn2+‐doped Ag2S quantum dots via co‐pyrolysis of silver and manganese single‐source precursors. The Mn2+ doping level was flexibly tuned in Ag2S quantum dots, which was confirmed by elemental analysis and electron paramagnetic resonance spectroscopy. The Mn2+ doping induced negligible change in the pristine monoclinic acanthite Ag2S crystal structure but significantly decreased the photoluminescent intensity. Mn2+‐doped Ag2S QDs exhibit second near‐infrared emission and ferromagnetic ordering, which show the potential applicability for multimodal fluorescence/MRI probes.