In applications such as atmospheric monitoring of greenhouse gases and pollutants, the detection and identification of trace concentrations of harmful gases is commonly achieved using nondispersive infrared (NDIR) sensors. These devices typically employ a broadband infrared emitter, thermopile detector, and spectrally selective bandpass filter tuned to the vibrational resonance of the target analyte. However, fabrication of these filters is costly and limited to a single frequency. This limitation introduces a fundamental trade-off, as broadening the optical passband width enhances sensitivity but compromises selectivity, whereas narrowing improves selectivity at the expense of sensitivity. In this work, we validate a filterless NDIR gas sensing approach utilizing a multipeak thermal emitter developed through an inverse design. This emitter enhances detection sensitivity by simultaneously targeting multiple absorption bands, demonstrated through the creation of a sensor designed for the C-H vibrational modes of propane (C3H8). Additionally, a second set of single-peak emitters was developed to showcase the capability of designing highly selective sensors operating within close spectral proximity. These emitters, targeting the stretching modes of carbon monoxide (CO) and carbon dioxide (CO2), exhibit quality factors (Q-factors) above 50 and minimal crosstalk, enabling accurate detection of the target gas without interference from gases with spectrally adjacent absorption bands. This is enabled by aperiodic distributed Bragg reflectors (a-DBRs), which achieve higher Q-factors with fewer layers than periodic Bragg reflectors. Experimental results demonstrate that this approach breaks the trade-off between sensitivity and selectivity.

In applications such as atmospheric monitoring of greenhouse gases and pollutants, the detection and identification of trace concentrations of harmful gases is commonly achieved using non-dispersive infrared (NDIR) sensors. These devices employ a broadband infrared emitter, thermopile detector, and a spectrally selective bandpass filter tuned to the vibrational resonance of the target analyte. However, the fabrication of these filters is costly and limited to a single frequency. This limitation introduces a fundamental tradeoff, as broadening the optical passband width enhances sensitivity but compromises selectivity, whereas narrowing improves selectivity at the expense of sensitivity. In this work, we validate a filterless NDIR approach using a multi-peak thermal emitter developed through inverse design. This emitter enhances detection sensitivity by targeting multiple absorption bands, demonstrated through the creation of a sensor designed for the C-H vibrational modes of propane. Additionally, a set of single-peak emitters were developed to showcase the capability of designing highly selective sensors operating within close spectral proximity. These emitters, targeting the stretching modes of carbon monoxide and carbon dioxide, exhibit Q-factors above 50 and minimal crosstalk, enabling accurate detection of the target gas without interference from gases with spectrally adjacent absorption bands. This is enabled by the implementation of an aperiodic distributed Bragg reflectors, which allows for higher Q-factors with fewer layers than a periodic Bragg reflector using the same materials and number of layers, thereby reducing fabrication complexity and cost. Experimental results validate that this approach breaks the tradeoff between sensitivity and selectivity. This work highlights the potential of optimized thermal emitters for more efficient and compact gas sensing applications.

The human dopamine transporter (DAT) is a presynaptic transmembrane protein that facilitates the reuptake of synaptically released dopamine. Several lines of evidence indicate that DAT dysfunction is linked to neuropsychiatric disorders. Moreover, the lateral membrane diffusion and clustering propensity of DAT are emergent properties that may factor into functional dopamine signaling. The disorder-associated DAT missense mutant A559V undergoes anomalous dopamine efflux (ADE) and increased lateral mobility and diffuse localization. The D2 dopamine autoreceptor short isoform (D2S), a popular antipsychotic target, signaling augments ADE in DAT A559V and may form stable DAT-D2S complexes. Using quantum dot (Qdot)-based single-molecule localization microscopy, we investigated the effect of D2S antagonism on DAT and DAT A559V membrane mobility in transfected HEK-293 cells. Single-color Qdot-DAT tracking shows phenotypic rescue of DAT A559V mobility upon D2S antagonism, while aberrant DAT A559V mobility is insensitive to ADE-linked CaMKII activity. Using two-color Qdot tracking of both the transporter and receptor, we report the first DAT-D2S colocalization lifetime in live cells. We show an increased propensity for both transporter types to colocalize with D2S, without impacting D2S diffusion speed under D2S antagonism. Downregulating D2S activity may stabilize DAT coconfinement in D2S microdomains on the cell surface.

Doped vanadium dioxide (VO2) nanoparticles (NPs) have significant potential for applications requiring temperature-dependent emissivity, reflectivity, or transmission. Thermochromic coatings in particular enable energy-saving smart windows and passive thermal radiators but are subject to tight performance constraints. A major challenge is preparing uniform layers of NPs, over large areas, with controllable size distributions and transition temperatures (T c). We describe the growth and transition characteristics of randomly distributed undoped and W-doped VO2 NPs formed by solid-state dewetting. Sizes and size distributions are controlled by anneal time, as particles grow via Smoluchowski aggregation before oxidizing into V2O5; shapes are determined by the interfacial energies between VO2 (V2O5) and the silicon substrate. Tungsten dopants concentrate at the NP surface, increasing the energy barrier for and slowing the rate of dewetting, aggregation, and oxidization. Surprisingly, the doped NPs exhibit lower T c and sharper hysteresis than comparably doped thin films. These results advance our capacity to engineer doped VO2 NPs, yield valuable insights into VO2-substrate interactions, and highlight the distribution of W-dopants in VO2 NPs.

Doping of colloidal nanocrystals offers versatile ways to improve their optoelectronic properties, with potential applications in photocatalysis and photovoltaics. However, the precise role of dopants on the interfacial charge transfer properties of nanocrystals remains poorly understood. Here, we use a Cu-doped InP@ZnSe quantum dot as a model system to investigate the dopant effects on both the intrinsic photophysics and their interfacial charge transfer by combining time-resolved transient absorption and photoluminescent spectroscopic methods. Our results revealed that the Cu dopant can cause the generation of the self-trapped exciton, which prolongs the exciton lifetime from 48.3 ± 1.7 to 369.0 ± 4.3 ns, facilitating efficient charge separation to slow electron and hole acceptors. However, hole localization into the Cu site alters their energetic levels, slowing hole transfer and accelerating charge recombination loss. This double-edged sword role of dopants in charge transfer properties is important in the future design of nanocrystals for their optoelectronic and photocatalytic applications.

Efforts to study intricate, higher-order cellular functions have called for fluorescence imaging under physiologically relevant conditions such as tissue systems in simulated native buffers. This endeavor has presented novel challenges for fluorescent probes initially designed for use in simple buffers and monolayer cell culture. Among current fluorescent probes, semiconductor nanocrystals, or quantum dots (QDs), offer superior photophysical properties that are the products of their nanoscale architectures and chemical formulations. While their high brightness and photostability are ideal for these biological environments, even state of the art QDs can struggle under certain physiological conditions. A recent method correlating electron microscopy ultrastructure with single-QD fluorescence has begun to highlight subtle structural defects in QDs once believed to have no significant impact on photoluminescence (PL). Specific defects, such as exposed core facets, have been shown to quench QD PL in physiologically accurate conditions. For QD-based imaging in complex cellular systems to be fully realized, mechanistic insight and structural optimization of size and PL should be established. Insight from single QD resolution atomic structure and photophysical correlative studies provides a direct course to synthetically tune QDs to match these challenging environments.

Cultural heritage artifacts present a distinct set of challenges when it comes to characterizing the material composition of extracted samples. Whatever samples are removed must be small to preserve the integrity of the artwork, and ideally, applied techniques should be nondestructive to allow samples to be saved for future use. Unfortunately, most nondestructive optical detection schemes are constrained to spatial resolutions set by the diffraction limit of light. Since many material-specific properties used for identification are dependent upon molecular vibrations and conductivity, this implies the need for spectral analysis in the infrared. The long wavelengths associated with infrared light can make it difficult to definitively identify materials when the sample composition varies at the length scales of nanometers. Nano-FTIR provides a unique solution whereby scattering-type scanning near-field optical microscopy is combined with a broadband illumination source for FTIR-like detection with subdiffraction spatial resolution (similar to 20 nm). The nondestructive nature of the technique makes it optimally suited to characterize art conservation samples while minimizing sample extraction by allowing individual samples to be characterized by multiple complementary techniques. In this work, the capabilities of nano-FTIR are evaluated in the study of surface coatings sampled from African wood sculptures, where the submicrometer scale of some of the layers makes the composition of the cross sections difficult to interpret using other established techniques. We show that the functional groups corresponding to different classes of organic coatings and inorganic pigments can be assigned based on point spectra, indicating that nano-FTIR holds great promise for the field of art conservation.

The incorporation of quantum dots in display technology has fueled a renewed interest in InP-based quantum dots, but difficulty controlling the Zn chemistry during shelling has stymied thick, even ZnSe shell growth. The characteristic uneven, lobed morphology of Zn-based shells is difficult to assess qualitatively and measure through traditional methods. Here, we present a methodological study utilizing quantitative morphological analysis of InP/ZnSe quantum dots to analyze the impact of key shelling parameters on InP core passivation and shell epitaxy. We compare conventional hand-drawn measurements with an open-source semi-automated protocol to showcase the improved precision and speed of this method. Additionally, we find that quantitative morphological assessment can discern morphological trends in morphologies that qualitative methods cannot. In conjunction with ensemble fluorescence measurements, we find that changes to shelling parameters that promote even shell growth often do so at the cost of core homogeneity. These results indicate that the chemistry of passivating the core and promoting shell growth must be balanced carefully to maximize brightness while maintaining emission color-purity.

Iron is indispensable for almost all forms of life but toxic at elevated levels1-4. To survive within their hosts, bacterial pathogens have evolved iron uptake, storage and detoxification strategies to maintain iron homeostasis1,5,6. Recent studies showed that three Gram-negative environmental anaerobes produce iron-containing ferrosome granules7,8. However, it remains unclear whether ferrosomes are generated exclusively by Gram-negative bacteria. The Gram-positive bacterium Clostridioides difficile is the leading cause of nosocomial and antibiotic-associated infections in the USA9. Here we report that C. difficile undergoes an intracellular iron biomineralization process and stores iron in membrane-bound ferrosome organelles containing non-crystalline iron phosphate biominerals. We found that a membrane protein (FezA) and a P1B6-ATPase transporter (FezB), repressed by both iron and the ferric uptake regulator Fur, are required for ferrosome formation and play an important role in iron homeostasis during transition from iron deficiency to excess. Additionally, ferrosomes are often localized adjacent to cellular membranes as shown by cryo-electron tomography. Furthermore, using two mouse models of C. difficile infection, we demonstrated that the ferrosome system is activated in the inflamed gut to combat calprotectin-mediated iron sequestration and is important for bacterial colonization and survival during C. difficile infection.

We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. Cobalt ferrites, however, generally show poor electronic conductivity at ambient temperatures, which limits their bifunctional catalytic performance in oxygen electrocatalysis. Our study reveals how the introduction of Mn ions promotes the conductivity of the cobalt ferrite electrode.

Surface waves can lead to intriguing transport phenomena. In particular, surface phonon polaritons (SPhPs), which result from coupling between infrared light and optical phonons, have been predicted to contribute to heat conduction along polar thin films and nanowires1. However, experimental efforts so far suggest only very limited SPhP contributions2-5. Through systematic measurements of thermal transport along the same 3C-SiC nanowires with and without a gold coating on the end(s) that serves to launch SPhPs, here we show that thermally excited SPhPs can substantially enhance the thermal conductivity of the uncoated portion of these wires. The extracted pre-decay SPhP thermal conductance is more than two orders of magnitude higher than the Landauer limit predicted on the basis of equilibrium Bose-Einstein distributions. We attribute the notable SPhP conductance to the efficient launching of non-equilibrium SPhPs from the gold-coated portion into the uncoated SiC nanowires, which is strongly supported by the observation that the SPhP-mediated thermal conductivity is proportional to the length of the gold coating(s). The reported discoveries open the door for modulating energy transport in solids by introducing SPhPs, which can effectively counteract the classical size effect in many technologically important films and improve the design of solid-state devices.

Photoelectrochemical (PEC) water splitting to produce hydrogen fuel was first reported 50 years ago 1 , yet artificial photosynthesis has not become a widespread technology. Although planar Si solar cells have become a ubiquitous electrical energy source economically competitive with fossil fuels, analogous PEC devices have not been realized, and standard Si p-type/n-type (p–n) junctions cannot be used for water splitting because the bandgap precludes the generation of the needed photovoltage. An alternative paradigm, the particle suspension reactor (PSR), forgoes the rigid design in favour of individual PEC particles suspended in solution, a potentially low-cost option compared with planar systems 2 , 3 . Here we report Si-based PSRs by synthesizing high-photovoltage multijunction Si nanowires (SiNWs) that are co-functionalized to catalytically split water. By encoding a p-type–intrinsic–n-type (p–i–n) superlattice within single SiNWs, tunable photovoltages exceeding 10 V were observed under 1 sun illumination. Spatioselective photoelectrodeposition of oxygen and hydrogen evolution co-catalysts enabled water splitting at infrared wavelengths up to approximately 1,050 nm, with the efficiency and spectral dependence of hydrogen generation dictated by the photonic characteristics of the sub-wavelength-diameter SiNWs. Although initial energy conversion efficiencies are low, multijunction SiNWs bring the photonic advantages of a tunable, mesoscale geometry and the material advantages of Si—including the small bandgap and economies of scale—to the PSR design, providing a new approach for water-splitting reactors.

We report the appearance of ferroelectric behavior arising from a room-temperature cation exchange of cadmium-based semiconductor nanoparticles. Fluorescence retention was achieved through protective CdS shelling before cation exchange with tin(IV) by containing defects in the CdS shell rather than the fluorescent CdSe cores. Ferroelectric response, measured using a Sawyer-Tower circuit, was kept constant, while fluorescence retention increases with an increase in the number of CdS monolayers. At 8 monolayers, fluorescence retention reached 99%, allowing for the addition of ferroelectric applications to the already ever-growing list of quantum dot applications.

The mechanism that governs the conversion of the Co-Prussian blue analogue (PBA) to Co2C was investigated and observed to exhibit lag phase growth behavior that can be fit to the autocatalytic kinetic model. The energetics and activation energies were extracted from the temperature-dependent data. The experimental results provide insight into how to control the size and crystallinity of Co2C, where shorter lag times and smaller sizes occur at higher reaction temperatures and longer times and larger sizes at lower temperatures. Investigation of temperature-dependent growth revealed an R-2 relationship, supporting a surface mediated growth model. In addition, low temperatures lead to higher polycrystallinity in the nanocrystal that grows within the PBA framework.

Single-phase MxCs (M = Fe, Co, and Ni) were prepared by solvothermal conversion of Prussian blue single source precursors. The single source precursor is prepared in water, and the conversion process is carried out in alkylamines at reaction temperatures above 200 °C. The reaction is scalable using a commercial source of Fe-PB. High-resolution transmission electron microscopy, X-ray photoelectron microscopy, and powder X-ray diffraction confirm that carbides have thin oxide termination but lack graphitic surfaces. Electrocatalytic activity reveals that Fe3C and Co2C are oxygen evolution reaction electrocatalysts, while Ni3C is a bifunctional [OER and hydrogen evolution reaction (HER)] electrocatalyst.

Semiconductor nanocrystals have become ubiquitous both in scientific research and in applied technologies related to light. When a nanocrystal absorbs a photon an electron-hole pair is created whose fate dictates whether the nanocrystal will be suitable for a particular application. Ultrafast spectroscopy provides a real-time window to monitor the evolution of the electron-hole pair. In this review, we focus on CdSe nanocrystals, the most-studied nanocrystal system to date, and also highlight ultrasmall nanocrystals, "standard nanocrystals" of different binary composition, alloyed nanocrystals, and core/shell nanocrystals and nanorods. We focus on four time-resolved spectroscopies used to interrogate nanocrystals: pump-probe, fluorescence upconversion, time-correlated single photon counting, and non-linear spectroscopies. The basics of the nanocrystals and the spectroscopies are presented, followed by a detailed synopsis of ultrafast spectroscopy studies performed on the various semiconductor nanocrystal systems.

Plasmonic photocatalysts have demonstrated promising potential for enhancing the selectivity and efficiency of important chemical transformations. However, the relative contributions of nonphotothermal (i.e., hot carrier) and photothermal pathways remain a question of intense current debate, and the time scale and extent of surface adsorbate temperature change are still poorly understood. Using p-type Cu2-xSe nanocrystals as a semiconductor plasmonic platform and adsorbed Rhodamine B as a surface thermometer and hot carrier acceptor, we measure directly by transient absorption spectroscopy that the adsorbate temperature rises and decays with time constants of 1.4 ± 0.4 and 471 ± 126 ps, respectively, after the excitation of Cu2-xSe plasmon band at 800 nm. These time constants are similar to those for Cu2-xSe lattice temperature, suggesting that fast thermal equilibrium between the adsorbates and nanocrystal lattice is the main adsorbate heating pathway. This finding provides insights into the transient heating effect on surface adsorbates and their roles in plasmonic photocatalysis.

Plasmonic semiconductors are an emerging class of low-cost plasmonic materials, and the presence of a bandgap and band-bending in these materials offer new opportunities to overcome some of the limitations of plasmonic metals. Here, we demonstrate that in a plasmonic p-n heterojunction (Cu2-xSe-CdSe) the near-IR excitation (1.1 eV) of the hole plasmon in the p-Cu2-xSe phase results in rapid hot electron transfer to n-CdSe, with an energy 2.2 eV above the Fermi level. This hot electron generation and energy upconversion process can be well-described by a photothermionic mechanism, where the presence of a bandgap in p-Cu2-xSe facilitates the generation of energetic photothermal electrons. The lifetime of the transferred electrons in Cu2-xSe-CdSe can reach ∼130 ps, which is nearly 100× longer than that of its metal-semiconductor counterpart. This result demonstrates a novel approach for harvesting the sub-bandgap near IR photons using plasmonic p-n junctions and the potential advantages of plasmonic semiconductors for hot carrier-based devices.

Plasmon induced hot carrier transfer is a promising novel approach for solar energy conversion, but its practical application is often hindered by its low efficiency. This work demonstrates an unprecedented quantum efficiency of plasmonic hot-electron transfer of up to 53 +/- 2% from 1.7 nm silver nanoparticles to anatase nanoporous TiO2 films at 400 nm excitation. This efficient hot-electron transfer consists of contributions of both hot electrons generated by plasmon decay through exciting Ag intraband transitions and Ag-to-TiO2 interfacial charge-transfer transitions. The efficiencies of both pathways increase at smaller Ag particle sizes from 5.9 to 1.7 nm, suggesting that decreasing particle sizes is a promising way toward efficient plasmonic hot-carrier extraction.

Understanding the role of dopant deactivation on plasmon frequency and extinction is important for the rational design of plasmonic semiconductor nanocrystals (PSNCs). Aliovalent dopants do not always contribute a free carrier to a localized surface plasmon resonance (LSPR) for many reasons, including the existence of a depletion region, the pinning of carriers at neutral defect sites, or even the formation of a secondary insulating microphase (inclusions) not observable in the powder X-ray diffraction (pXRD). Here, we investigate such possibilities and their role in determining the LSPR frequency of Al-, Ga-, and In-doped ZnO NCs. Elemental analysis, pXRD, and absorption measurements are utilized to examine the impact of dopant incorporation on the resulting properties. Both simple and advanced effective mass Drude models are used to fit the mid-infrared plasmons, while one-electron oxidant chemical titrations are used as an independent measure of the free electron concentrations. The results of these analyses indicate that dopant/host lattice mismatch leads to inefficient carrier generation for aliovalent substitution, potentially due to local spinel-like inclusions. Smaller dopant ions are more likely to incorporate interstitially and form spinel phases, which results in an increased number of pinned carriers. Improved size matching from Al3+ to In3+ results in increased substitution efficiency and subsequently higher free carrier concentrations and LSPR frequencies. Drude model correction factors are calculated for each sample and compared to the literature value for n-ZnO determined via full band structure calculations. Each dopant is shown to have a unique correction factor, further illustrating the effect of differing ionic radii on the resulting LSPR.