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Traditional semiconductors are known to exhibit excellent electrical properties but oversized lattice thermal conductivities, thus limiting their thermoelectric performance. Herein, we have discovered a low-energy allotrope of those traditional semiconductors. Compared with the wurtzite structure, the lattice thermal conductivity is reduced by more than five times in the haeckelite structure. This is attributed to the softening of acoustic phonon modes and concurrently enhanced anharmonicity in the haeckelite structure. Benefiting from the suppressed lattice thermal conductivity while retaining the excellent electrical properties of wurtzite structure, haeckelite compounds have been proven to be a novel category of high-performance thermoelectric materials. As an excellent representative, haeckelite CdTe exhibits a peak figure of merit approaching 1.3 at n-type doping and high temperature, which experiences a 3-fold improvement compared with its wurtzite counterpart. This work provides an alternative pathway of engineering the lattice thermal conductivities of traditional semiconductors toward superior thermoelectric properties.

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Traditional semiconductor quantum dots of groups II-VI are key ingredients of next-generation display technology. Yet, the majority of them contain toxic heavy-metal elements, thus calling for alternative light-emitting materials. Herein, we have explored three novel categories of multicomponent compounds, namely, tetragonal II-III2-VI4 porous ternary compounds, cubic I2-II3-VI4 ternary compounds, and cubic I-II-III3-V4 quaternary compounds. This is achieved by judicious introduction of a "super atom" perspective and concurrently varying the solid-state lattice packing of involved super atoms or the population of surrounding counter cations. Based on first-principles calculations of 392 candidate materials with designed crystal structures, 53 highly stable materials have been screened. Strikingly, 34 of them are direct-bandgap semiconductors with emitting wavelengths covering the near-infrared and visible-light regions. This work provides a comprehensive database of highly efficient light-emitting materials, which may be of interest for a broad field of optoelectronic applications.

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This study aimed to construct a novel DNA triplex molecular switch modified with DNA tetrahedron (DTMS-DT) with sensitive response to extracellular pH using a DNA tetrahedron as the anchoring unit and DNA triplex as the response unit. The results showed that the DTMS-DT had desirable pH sensitivity, excellent reversibility, outstanding anti-interference ability, and good biocompatibility. Confocal laser scanning microscopy suggested that the DTMS-DT could not only be stably anchored on the cell membrane but also be employed to dynamically monitor the change in extracellular pH. Compared with the reported probes for extracellular pH monitoring, the designed DNA tetrahedron-mediated triplex molecular switch exhibited higher cell surface stability and brought the pH-responsive unit closer to the cell membrane surface, making the results more reliable. In general, developing the DNA tetrahedron-based DNA triplex molecular switch is helpful for understanding and illustrating the pH dependent cell behaviors and disease diagnostics.

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Colloidal quantum dots (QDs) of groups II-VI and III-V are key ingredients for next-generation light-emitting devices. Yet, many of them are heavy-element-containing or indirect bandgap, causing limited choice of environmental friendly efficient light-emitting materials. Herein, we resolve this issue by exploring potential derivatives of the parent semiconductors, thus expanding the material space. The key to success is the discovery of a principle for designing those materials, namely, cation stabilizing charged cluster network. Guided by this principle, three novel categories of cubic materials have been predicted, namely, porous binary compounds, I-II-VI ternary compounds, and I-II-III-V quaternary compounds. Using first-principles calculations, 65 realistic highly stable candidate materials have been theoretically screened. Their structural and compositional diversity enables a wide tunability of emitting wavelength from far-infrared to ultraviolet region. This work enriches the family of tetrahedral semiconductors and derivatives, which may be of interest for a broad field of optoelectronic applications.

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Environmentally friendly colloidal quantum dots (QDs) of groups III-V are in high demand for next-generation high-performance light-emitting devices for display and lighting, yet many of them (e.g., GaP) suffer from inefficient band-edge emission due to the indirect bandgap nature of their parent materials. Herein, we theoretically demonstrate that efficient band-edge emission can be activated at a critical tensile strain γc enabled by the capping shell when forming a core/shell architecture. Before γc is reached, the emission edge is dominated by dense low-intensity exciton states with a vanishing oscillator strength and a long radiative lifetime. After γc is crossed, the emission edge is dominated by high-intensity bright exciton states with a large oscillator strength and a radiative lifetime that is shorter by a few orders of magnitude. This work provides a novel strategy for realizing efficient band-edge emission of indirect semiconductor QDs via shell engineering, which is potentially implemented employing the well-established colloidal QD synthesis technique.

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Quantum dots (QDs) have been considered as the promising fluorescent labeling material, which is expected to meet the requirement of high-sensitivity detection in clinical diagnostics. Some common metal ions are known to affect the stability and fluorescence properties of QDs, but scarcely any systematic research has been done about their impacts on QD-based bio-detection. By evaluating the effect of Ca2+ metal ions on the properties of aqueous QDs, a new metal ion-QD fluorescence signal amplification sensor (i.e., Ca2+-QD-fluorescence-linked immunosorbent assay, Ca2+-QD-FLISA) has been developed for the detection of inflammatory biomarkers with high sensitivity. Compared with the common QD-FLISA, the detection sensitivity for CRP of Ca2+-QD-FLISA was improved by a 4-fold of magnitude to 0.23 ng/mL, and this assay showed good selectivity, high accuracy, and excellent repeatability. The versatility of the QD-FLISA method were also validated by using different metal ion-QD probes (Ca2+, Mg2+, Ba2+, Fe2+, and Mn2+) to detect CRP, serum amyloid A (SAA), and procalcitonin (PCT). The significant improvement in detection sensitivity was achieved due to the crosslinking of aqueous QDs by Ca2+ ions to enhance fluorescence and at the same time promote antigen-antibody binding efficiency. The present study illustrates the versatility of metal ion-QD-FLISA as a simple and effective method to detect a wide range of biomarkers with high sensitivity and accuracy.

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Environmentally friendly blue-emitting ZnSe quantum dots (QDs) are in high demand for next-generation light-emitting devices. Yet, they suffer longstanding optical instability issues under aerobic conditions. Herein, we have demonstrated the existence of oxidization or hydroxylation on the QD surface when QDs are subjected to oxygen exposure, which potentially introduces highly localized in-gap states. Those states result in a dense number of surface-related, weak-intensity "dark" exciton states at the emission edge. Remarkably, there exists a critical diameter (Dc ≈ 8.5 nm) at which the deepest trap level reaches resonance with the highest occupied molecular orbital state. Beyond this critical diameter, the effects of those trap states are minimized, and the emission edge is dominated by high-intensity, bulk-to-bulk-like "bright" exciton states. The present work provides a novel strategy for designing highly stable QD emitters via size engineering, which are broadly applicable to other closely related QD systems.

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Establishment of a stable analytical methodology with high-quality results is an urgent need for screening cancer biomarkers in early diagnosis of cancer. In this study, we incorporate holographic optical tweezers with upconversion luminescence encoding to design an imageable suspension array and apply it to conduct the detection of two liver cancer related biomarkers, carcinoembryonic antigen and alpha fetal protein. This bead-based assay is actualized by forming a bead array with holographic optical tweezers and synchronously exciting the upconversion luminescence of corresponding trapped complex beads fabricated with a simple one-step sandwich immunological recognition. Owing to the fact that these flowing beads are stably trapped in the focal plane of the objective lens which tightly converges the array of the laser beams by splitting a 980 nm beam using a diffraction optical element, a fairly stable excitation condition is achieved to provide reliable assay results. By further taking advantage of the eminent encoding capability of upconversion nanoparticles and the extremely low background signals of anti-Stokes luminescence, the two targets are well-identified and simultaneously detected with quite sound sensitivity and specificity. Moreover, the potential on-demand clinical application is presented by employing this approach to respond the targets toward complex matrices such as serum and tissue samples, offering a new alternative for cancer diagnosis technology.

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As an emerging fascinating fluorescent nanomaterial, carbon nanodots (CDs) have attracted much attention owing of their unique properties such as small size, antiphotobleaching, and biocompatibility. However, its use in biomedical analysis is limited because of its low quantum yield. Herein, we constructed a dual amplification fluorescence sensor by incorporating immunohybridization chain reaction (immuno-HCR) and metal-enhanced fluorescence (MEF) of CDs for the detection of alpha fetal protein (AFP). The immunoplasmonic slide and detection antibodies-conjugated oligonucleotide initiator are served to capture and probe AFP molecules, respectively. Then, CD-tagged hairpin nucleic acids were introduced to trigger the HCR, in which the hairpin nucleic acid and oligonucleotide initiator are complementary. The interaction between CDs and the gold nanoisland film greatly improves the radiative decay rate, increases the quantum yield, and enhances the fluorescence emission of the CDs. Furthermore, the HCR provides secondary amplification of fluorescence intensity. Therefore, the MEF-capable immunohybridization reactions provide obvious advantages and result in exceptional sensitivity. In addition, the sandwich immunoassay method offers high specificity. The results show a wide linearity between the fluorescence intensity and AFP concentration over 5 orders of magnitude (0.0005-5 ng/mL), and the detection limit reaches as low as 94.3 fg/mL. This method offers advantages of high sensitivity and reliability, wide detection range, and versatile plasmonic chips, thus presenting an alternative for the technologies in biomedical analysis and clinical applications.

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A three-layer core-shell nanostructure consisting of a silver core, a silica spacer, and a fluorescent dye RuBpy-doped outer silica layer was fabricated, and the optimal metal-enhanced fluorescence (MEF) distance was explored through adjusting the thickness of the silica spacer. The results show that the optimal distance is ∼10.4 nm with the maximum fluorescence enhancement factor 2.12. Then a new target-triggered MEF 'turn-on' strategy based on the optimized composite nanoparticles was successfully constructed for quantitative detection of prostate specific antigen (PSA), by using RuBpy as the energy donor and BHQ-2 as the acceptor. The hybridization of the complementary DNA of PSA-aptamer immobilized on the surface of the MEF nanoparticles with PSA-aptamer modified with BHQ-2, brought BHQ-2 in close proximity to RuBpy-doped silica shell and resulted in the decrease of fluorescence. In the presence of target PSA molecules, the BHQ-PSA aptamer is dissociated from the surface of the nanoparticles with the fluorescence switched on. Therefore, the assay of PSA was achieved by measuring the varying fluorescence intensity. The results show that PSA can be detected in the range of 1-100 ng ml-1 with a detection limit of 0.20 ng ml-1 (6.1 pM), which is 6.7-fold increase of that using hollow RuBpy-doped silica nanoparticles. Moreover, satisfactory results were obtained when PSA was detected in 1% serum.

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The world health organization figures show prostate cancer in developed countries has been the second primary cause of cancer mortality following lung cancer for the men. So, early and sensitive diagnosis of cancer is very important before it spreads out to the other organs of the body. It is well-known that prostate-specific antigen (PSA) is the most specific and efficient tumor marker for the diagnosis of prostate cancer. Herein, we successfully fabricated core-shell composite fluorescent nanoparticle Ag@SiO2@SiO2-RuBpy which provide a photoluminescence enhancement of up to ~3-fold when the separation distance between the surface of silver core and the center of the third RuBpy doped silica shell is about 10nm. These core-shell MEF-capable nanoparticles have obvious advantages. The interaction between the doped RuBpy molecules in the outer silica layer and the silver core, greatly improves the excitation efficiency and enhances the fluorescence intensity. Importantly, the presence of silica can reduce the self-quenching of RuBpy, which makes larger amounts of RuBpy incorporated into the silica shell. In addition, the shell protects the RuBpy against collisional quenching and irreversible photodegradation and provides abundant hydroxyl for easy conjugation. After that a highly sensitive, specific and reliable strategy based on metal-enhanced fluorescence and magnetic separation was applied for the detection of PSA in both buffer and serum. The process could be rapidly accomplished, in which the immunomagnetic nanospheres (IMNs) and immunofluorescent nanoparticles (IFNs) were used to capture and identify the target molecules simultaneously. A good linear relationship between the fluorescence intensity and the concentration of PSA (0.1-100ng/mL) with a detection limit 27pg/mL was obtained.

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Based on the remarkable difference between the interactions of carbon nanoparticles (CNPs) oxide with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), and the fact that fluorescence of DNA-stabilized silver nanoclusters (AgNCs) can be quenched by CNPs oxide, DNA-functionalized AgNCs were applied as label-free fluorescence probes and a novel fluorescence resonance energy transfer (FRET) sensor was successfully constructed for the detection of human immunodeficiency virus (HIV) DNA sequences. CNPs oxide were prepared with the oxidation of candle soot, hence it is simple, time-saving and low-cost. The strategy of dual AgNCs probes was applied to improve the detection sensitivity by using dual- probe capturing the same target DNA in a sandwich mode and as the fluorescence donor, and using CNPs oxide as the acceptor. In the presence of target DNA, a dsDNA hybrid forms, leading to the desorption of the ssDNA-AgNCs probes from CNPs oxide, and the recovering of fluorescence of the AgNCs in a HIV-DNA concentration-dependent manner. The results show that HIV-DNA can be detected in the range of 1-50nM with a detection limit of 0.40nM in aqueous buffer. The method is simple, rapid and sensitive with no need of labeled fluorescent probes, and moreover, the design of fluorescent dual-probe makes full use of the excellent fluorescence property of AgNCs and further improves the detection sensitivity.

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