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Yellow fluorescent carbon dots (Y-CDs) were prepared via microwave method using chitosan and o-phenylenediamine as the main raw materials. The obtained Y-CDs possesses good water solubility, excellent biocompatibility and luminous stability. During the microwave pyrolysis carbonization process, the surface of Y-CDs was modified with the functional groups such as amino and carboxyl, which can bind to Al 3+ by forming complexes, further improving the selectivity and sensitivity of the Al 3+ detection. And the fluorescence of Y-CDs was quenched by Al 3+ by static quenching process. More importantly, Y-CDs as fluorescent sensor was further applied for the determination of Al 3+ in the real water samples with high reliability and accuracy. In addition, Y-CDs present potential application in biological imaging. The cultivated zebrafish embryos with Y-CDs displayed clearly in vivo uptake and metabolic fluorescence images, further confirming its low toxicity and excellent biocompatibility., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A core-satellite nanocomposite was prepared by encapsulating the photostable blue carbon dots (BCDs) in the core of silica as the reference signal readout, and the target-sensitive gold nanoclusters (AuNCs) covalently linked to the surface of silica as the respond signal readout. The nanocomposite (BCD@SiO 2 @AuNC) was used as a ratiometric fluorescent sensor to realize the selective detection of Gram-negative bacteria. The detection principle was based on the quenching of Cu 2+ toward AuNCs and the reduction of Gram-negative bacteria toward Cu 2+ . The sensor exhibited good selectivity toward Gram-negative bacteria owing to the copper-homeostasis mechanism possessed by the bacteria. The sensor demonstrated linear response to the logarithm concentration of Gram-negative bacteria with determination coefficients higher than 0.912. The feasibility of the sensor was verified by analysis of Gram-negative bacteria in eggshell, swimming pool water, as well as Chinese cabbage samples with recoveries ranging from 93.9% to 109%., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Serious threat from pesticide residues to the ecosystem and human health has become a global concern. Developing reliable methods for monitoring pesticides is a world-wide research hotspot. Carbon dots (CDs) with excellent photostability, low toxicity, and good biocompatibility have been regarded as the potential substitutes in fabricating various optical sensors for pesticide detection. Based on the relevant high-quality publications, this paper first summarizes the current state-of-the-art of the synthetic and modification approaches of CDs. Then, a comprehensive overview is given on the recent advances of CDs-based optical sensors for pesticides over the past five years, with a particular focus on photoluminescent, electrochemiluminescent and colorimetric sensors regarding the sensing mechanisms and design principles by integrating with various recognition elements including antibodies, aptamers, enzymes, molecularly imprinted polymers, and some nanoparticles. Novel functions and extended applications of CDs as signal indicators, catalyst, co-reactants, and electrode surface modifiers, in constructing optical sensors are specially highlighted. Beyond an assessment of the performances of the real-world application of these proposed optical sensors, the existing inadequacies and current challenges, as well as future perspectives for pesticide monitoring are discussed in detail. It is hoped to provide powerful insights for the development of novel CDs-based sensing strategies with their wide application in different fields for pesticide supervision., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Arginine kinase (AK) is one of the most important allergens in shrimp products. Herein, a novel immunoassay for quantitation of AK was developed using the antibody modified gold nanoparticle (AuNP) and quantum dot (QD). When the first antibody modified AuNP (AuNP-Ab1) was bridged by AK with the secondary antibody modified QD (QD-Ab2), fluorescence resonance energy transfer (FRET) would occur between the AuNP and QD, which led to a decrease in fluorescent signals. The decrease in fluorescence intensity was found to correlate linearly with the log of AK concentration in the range of 1.0 × 10 -6 -1.0 × 10 -3 mg/mL (R 2  = 0.9909) and the detection limit was 0.11 ng/mL. The immunoassay was further proved to have encouraging specificity, precision and accuracy. Compared with existing methods, this study provided a promising approach to develop a highly sensitive and selective detection method for AK in shrimp related food samples., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Near-infrared electrochemiluminescence (NIR ECL) luminophores are strongly anticipated in ECL bioimaging and spectrum-resolved multiplexing assays. Herein, bovine serum albumin-stabilized Ag nanoclusters (BSA-Ag NCs) are demonstrated promising NIR ECL performance, exhibiting strong anodic ECL spectrum peak at 904 nm in aqueous medium. The ECL intensity of BSA-Ag NCs-triethanolamine system was enhanced 3.2 times by adding TiO 2 nanoparticles as co-reactant accelerator. In a spectrum-resolved triplex-color ECL multiplexing immunoassay, CdSe NCs, CdTe NCs and BSA-Ag NCs were used as the ECL tags, carbohydrate antigen 125 (CA125), carbohydrate antigen 19-9 (CA19-9) and cardiac troponin I (cTnI) were chosen as model analytes. The ECL peaks of three antigen-NCs pairs were simultaneously measured via one ECL potential scan. The composite of carbon nanotubes-TiO 2 nanoparticles-chitosan was served as the conductivity and co-reactant accelerators, enhancing the ECL intensity by 16 folds. With the integral intensity over the ECL peaks as the analytical signal to improve further the signal-to-noise ratio, the limits of detection were 0.035 mU mL -1 for CA125, 0.087 mU mL -1 for CA19-9, and 0.016 pg mL -1 for cTnI, respectively., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Green microalgae are promising and sustainable bioenergy and biomass feedstocks, that specifically utilize blue and red light for photosynthesis. Using carbon dots (CDs) to optimize photoluminescence is an attractive strategy for enhancing microalgal bioresource production; however, CD synthesis traditionally requires harsh conditions and laborious procedures. Little research has focused on developing CDs with tunable emission that precisely satisfy photosynthetic requirements. In this work, we directionally prepared non-toxic CDs using a simple method, which could adsorb light at spectra 500-600 nm and emit red light at 580-700 nm. CDs significantly promoted microalgae (Chlorella) growth by ~15%. Meanwhile, potential intracellular bioresources, pigments, carbohydrates, proteins, and lipids were generally enhanced. CDs, combined with an extracellular polymeric substance of microalgal cells, served as numerous micro-bulbs for Chlorella irradiation to sustainably provide optimized light. In this context, photosystems I and II were both stimulated. As such, we prepared CDs with tunable emission, which could significantly enhance microalgae and bioresource production., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

We reported a facile strategy to assemble a ratiometric nanosensor for the ovalbumin (OVA) fluorescence determination and meanwhile it can be utilized for selective visual identification by naked eyes with fluorescent test papers under 365 nm UV lamp. The nanosensor was prepared through simply mixing blue color carbon dots (CDs) and green color core-shell imprinted polymers. Blue CDs were used directly as the internal reference without participating in the imprinting process and modified molecularly imprinted polymers (MIPs) were synthesized by post-imprinting, using fluorescein isothiocyanate (FITC) as fluorescence enhanced signal. Upon the addition of different concentrations of OVA, the fluorescence intensity of FITC was enhanced, while the fluorescence intensity of CDs was almost unchanged, leading to a detection limit as low as 15.4 nM. Accordingly, the fluorescence color was gradually changed from blue to dark olive green to green with naked eyes observation. Moreover, the ratiometric nanosensor was successfully applied to detect OVA in the human urine samples with satisfactory recoveries attaining of 92.0-104.0% with relative standard deviation (RSD) of 3.3-3.9% and 93.3-101.0% with RSDs of 2.7-3.8% for the spiked chicken egg white samples. This strategy reported here opens a novel pathway for biomacromolecule detection in real applications and can realize the visual observation on fluorescent test papers., (Copyright © 2020 Elsevier B.V. All rights reserved.)

We describe a simple and effective strategy to construct a molecular imprinting ratiometric fluorescence sensor (MIR sensor) for the visual detection of bovine hemoglobin (BHb) used as a model protein. The sensor was prepared by simply mixing the solution of green and red CdTe quantum dots (QDs), which were embedded in core-shell structured molecularly imprinted polymers and silica nanoparticles, respectively. The resultant hybrid MIR sensor can selectively bind with BHb and thus quench the fluorescence of the green QDs, while the red QDs wrapped with silica are insensitive to BHb with the fluorescence intensity unchanged. As a result, a continuous obvious fluorescence color change from green to red can be observed by naked eyes, with the detection limit of 9.6 nM. Moreover, the MIR sensor was successfully applied to determine BHb in bovine urine samples with satisfactory recoveries at three spiking levels ranging from 95.7 to 101.5%, indicating great potential application for detecting BHb in real samples. This strategy of using different fluorescence emission materials incorporated to construct a ratiometric fluorescence sensor is reasonable and convenient, which can be extended to the preparation of other ratiometric fluorescence systems for targeted analytes.

The toxicity of CdTe QDs modified with three different ligands, namely mercaptopropionic acid (MPA), N-acetyl-L-cysteine (NAC), and glutathione (GSH), were investigated via microcalorimetric, spectroscopic, and microscopic methods. The three ligand-modified QDs have nearly identical hydrodynamic size. The results of the calorimetric experiments and optical density measurements indicate that the QDs inhibited the growth of Gram-negative Escherichia coli. The toxicity order of the three QDs is MPA-CdTe QDs>GSH-CdTe QDs>NAC-CdTe QDs. The inhibitory effects of the QDs, cadmium chloride (CdCl(2)), MPA, and the CdCl(2) and MPA mixture on E. coli growth indicate that the toxicity mechanism of QDs may be related to their bacterial adhesion. When dispersed in the cell suspensions, QDs tend to have their high surface energy reduced through adsorption to the bacterial surface, as confirmed by transmission electron microscopy and inductively coupled plasma atomic emission spectroscopy results. Furthermore, the effect of QDs on the membrane fluidity and permeability was investigated. GSH-CdTe QDs have a greater effect on the membrane function of E. coli than those of MPA-CdTe and NAC-CdTe QDs. This result may be attributed to the stronger lipophilicity of GSH compared with those of MPA and NAC., (Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.)

We report on a detailed analysis of the effects of doping on the main device parameters of In(0.5)Ga(0.5)As/GaAs/Al(0.2)Ga(0.8)As quantum dots-in-a-well infrared photodetectors. Due to the relatively large conduction band offset of GaAs/Al(0.2)Ga(0.8)As (167 meV) transitions from wetting layer to quantum well states are observed for the highly doped devices. Since increasing the doping concentration fills the quantum dot states, electrons are forced to occupy the one-dimensional wetting layer states and therefore have quantum-well-like properties. This has facilitated a comparative study of the effects of three-dimensional and one-dimensional confinement of electrons on device parameters such as the responsivity and dark current by studying one particular detector structure with different doping concentrations of the active region.

The use of mesoporous silicon particles for drug delivery has been widely explored thanks to their biodegradability and biocompatibility. The ability to tailor the physicochemical properties of porous silicon at the micro- and nanoscale confers versatility to this material. A method for the fabrication of highly reproducible, monodisperse, mesoporous silicon particles with controlled physical characteristics through electrochemical etching of patterned silicon trenches is presented. The particle size is tailored in the micrometer range and pore size in the nanometer range, the shape from tubular to discoidal to hemispherical, and the porosity from 46 to over 80%. In addition, the properties of the porous matrix are correlated with the loading of model nanoparticles (quantum dots) and their three-dimensional arrangement within the matrix is observed by transmission electron microscopy tomography. The methods developed in this study provide effective means to fabricate mesoporous silicon particles according to the principles of rational design for therapeutic vectors and to characterize the distribution of nanoparticles within the porous matrix.

We report on a theoretical study of the relationship between interdiffusion and the conduction band optical absorption of In(Ga)As/GaAs quantum dots. Quantum dot geometries are progressively interdiffused based on Fick's model and the quantum dot strain, band structure and optical absorption cross-section are calculated numerically. Quantifying the effects of interdiffusion on quantum dot optical absorption is important for applications that utilize post-growth techniques such as selective area intermixing. [ABSTRACT FROM AUTHOR]

In this work, rapid thermal annealing was performed on InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700 °C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800 °C, in addition to the largely redshifted photoresponse peak of 7.4 μm (compared with the 6.1 μm of the as-grown QDIP), a high energy peak at 5.6 μm (220 meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy. [ABSTRACT FROM AUTHOR]

In this article the effect of rapid thermal annealing (RTA) on a 30 stacked InAs/GaAs, molecular beam epitaxially grown quantum dot infrared photodetector (QDIP) device is studied. Temperatures in the range of 600–800 °C for 60 s, typical of atomic interdiffusion methods are used. After rapid thermal annealing the devices exhibited large dark currents and no photoresponse could be measured. Double crystal x-ray diffraction and cross sectional transmission electron microscopy studies indicate that this could be the result of strain relaxation. V-shaped dislocations which extended across many quantum dot (QD) layers formed in the RTA samples. Smaller defect centers were observed throughout the as-grown sample and are also likely a strain relaxation mechanism. This supports the idea that strained structures containing dislocations are more likely to relax via the formation of dislocations and/or the propagation of existing dislocations, instead of creating atomic interdiffusion during RTA. Photoluminescence (PL) studies also found that Si related complexes developed in the Si doped GaAs contact layers with RTA. The PL from these Si related complexes overlaps and dominates the PL from our QD ground state. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The article investigates and compares two of the most important intermixing techniques, ion implantation and impurity free vacancy disordering, in InGaAs/(Al)GaAs quantum well (QW) and quantum dot (QD) structures. For ion implantation induced intermixing, arsenic implantation has been performed and the amount of interdiffusion created has been found to vary as a function of implantation dose and temperature. Impurity free vacancy disordering has also been enhanced by deposition of SiO2 in both QW and QD structures and annealing at different temperatures. In order to obtain large differential energy shifts for device integration using both methods, the essential issue of suppression of thermal interdiffusion using a TiO2 capping layer has also been addressed.

Cross-sectional scanning spreading resistance microscopy (SSRM) is used to investigate stacked InGaAs/GaAs quantum dot (QD) structures with different doping schemes. Spatially resolved imaging of the QDs by SSRM is demonstrated. The SSRM contrast obtained for the QD layers is found to depend on doping in the structure. In the undoped structures both QD-layers and QDs within the layers could be resolved, while in the doped structures the QD layers appear more or less uniformly broadened. The origin of the SSRM contrast in the QD layer in the different samples is discussed and correlated with doping schemes. [ABSTRACT FROM AUTHOR]

We report the postgrowth fabrication of two-color InGaAs/GaAs quantum dot infrared photodetectors (QDIPs). By capping half of the as-grown QDIP structure with titanium dioxide (TiO2) and performing rapid thermal annealing under the optimized condition, a blueshifted photoluminescence from the uncapped region was obtained compared with the TiO2 covered region. The corresponding device spectral photoresponse from the two adjacent regions exhibited a shift of 0.8 μm around the wavelength of 6 μm. This is a result of the simultaneous promotion and suppression of thermal interdiffusion during rapid thermal annealing. [ABSTRACT FROM AUTHOR]

We report on the effects of the quantum well (QW) thickness on the spectral response and other characteristics of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. The main device properties are observed to have a strong dependence on the QW parameters. [ABSTRACT FROM AUTHOR]

We report on the spectral behavior of two different quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. In0.5Ga0.5As quantum dots embedded in an In0.15Ga0.85As/GaAs quantum well (QW) or a GaAs/Al0.2Ga0.8As QW have been incorporated into photodetectors and were characterized. A spectral response in the 3–5 μm atmospheric window has been achieved by adopting the GaAs/Al0.2Ga0.8As QW. [ABSTRACT FROM AUTHOR]

The effect of GaP strain compensation layers was investigated on ten-layer InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) grown by metal-organic chemical-vapor deposition. Compared with the normal QDIP structure, the insertion of GaP has led to a narrowed spectral linewidth and slightly improved detector performance. A more significant influence of GaP was observed after the structure was annealed at various temperatures. While a similar amount of wavelength tuning was obtained, the GaP QDIPs exhibited much less degradation in device characteristics with increasing annealing temperature. [ABSTRACT FROM AUTHOR]

Impurity-free disordering (IFD) of the InAs quantum dots (QDs) capped with either an InP layer or an InGaAs/InP bilayer is studied. The samples are coated with a SiO2 or TiO2 dielectric layer followed by rapid thermal annealing at 700, 750, 800, and 850 °C for 30 s. A large differential energy shift of 157 meV is induced by SiO2 in the QDs capped with an InGaAs/InP bilayer. Contrary to the reported results on the suppression of intermixing of GaAs based QDs by TiO2, the authors find that intermixing of InAs/InP QDs is promoted by TiO2. X-ray photoelectron spectroscopy depth profiles show that both In and P outdiffuse to a TiO2 layer whereas Ga, In, and P outdiffuse to a SiO2 layer leading to different degrees of intermixing. The results indicate that a group V interstitial diffusion mechanism might be responsible for IFD of InAs/InP QDs. [ABSTRACT FROM AUTHOR]

We report the growth by low-pressure metal-organic chemical vapor deposition, fabrication, and characterization of ten-layer In0.5Ga0.5As/GaAs quantum dot infrared photodetectors. Normal incidence photoresponse of the detector was obtained at 5.9 µm. The 77-K peak responsivity was 5.6 mA/W with the detectivity D* of 1.2 × 109 cm · Hz½/W at the bias of 0.4 V. [ABSTRACT FROM AUTHOR]

Thermal-stress controlled interdiffusion in InGaAsN/GaAs quantum dots (QDs) has been studied by deposition of titanium oxide (TiO2) layers combined with rapid thermal annealing. Without TiO2 cap layers, blueshifting of the band gap from 1.033 to 1.180 eV at 77 K has been observed after annealing at 850 °C for 30 s due to the thermal interdiffusion. The thermal interdiffusion has been effectively suppressed by depositing TiO2 layers on the samples without degrading the photoluminescence properties. By a combination of annealing temperature and TiO2 thickness, controlled blueshifting of the band gap has been achieved. We suggest that the mechanism of suppression of thermal interdiffusion is the thermal stress imposed on the QD structure generated by TiO2 layers during annealing. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]