Quantum Dots Research Articles

Enhancing the quantum yield and electrochemical properties of carbon quantum dots via optimized hydrothermal treatment using cellulose nanocrystals as precursors

Carbon quantum dots (CQDs) are receiving increasing attention due to their tunable redox activity, abundant surface functional groups, and excellent aqueous dispersion. However, their low quantum yield remains a significant impediment to their synthesis and practical application. In the present work, cellulose nanocrystals (CNCs) were utilized as precursors for the optimized hydrothermal synthesis of CQDs. Subsequently, the synthesized CQDs were electrodeposited onto a carbon-coated surface. The influence of hydrothermal temperature and time on the quantum yield and electrochemical properties of CQDs was systematically explored. The successful synthesis of CQDs displayed an average particle size of 5 nm, approximately. The quantum yield was enhanced from 14.35 % to 23.7 % as the hydrothermal temperature increased from 180 °C to 230 °C. Additionally, the electrochemical properties of the composite films were investigated. Electrochemical assessments demonstrated an increase in specific capacitance from 60.4 mF·cm−2 to 65.2 mF·cm−2 with an elevation in temperature from 180 °C to 210 °C. Remarkably, the CQDs displayed higher e CQDs, showcasing their substantial potential for supercapacitor applications.

Attaining a wide photoluminescence Stokes-shift of carbon dots obtained from waste biomass

Owing to the tremendous physicochemical and quantum confinement characteristics of carbon quantum dots (CQDs), they have revealed exciting and essential visions in the field of energy conversion and energy storage. However, due to their low photoluminescence quantum yield (PLQY) and/or short Stokes-shift, limits their application in photovoltaic (PV). In this regard, a novel and cost-effective method was used to synthesize the CQDs using waste biomass. Furthermore, a comprehensive study was made to explore the applicability of the CQDs as photon downconverters/downshifters in PVs. The average size of the CQDs are 5.1, 4.4, and 3.9 nm for the synthesis temperature of 160, 180, and 200 ℃, respectively. The EDS analysis revealed that C, O, Mg, Na, Cl, and K are present in all the CQDs. The PL emission peak position is blue-shifted with the rise in the synthesis temperature. The Stokes-shift is reduced with a rise in the synthesis temperature. The highest Stokes-shift was obtained at excitation wavelength of 300 nm for CQDs synthesized at 160 ℃. The PLQY increased by 3.5 and 7.2-folds for the rise in the temperature from 160 to 180 and 200 ℃, respectively. The investigation revealed that the applicability of CQDs can be enriched via the selection of the synthesis parameters.

Correcting on-chip distortion of control pulses with silicon spin qubits

Abstract In semiconductor quantum dot systems, pulse distortion is a significant source of coherent errors, which impedes qubit characterization and control. Here, we demonstrate two calibration methods using a two-qubit system as a detector to correct distortion and calibrate the transfer function of the control line. Both methods are straightforward to implement, robust against noise, and applicable to a wide range of qubit types. The two methods differ in correction accuracy and complexity. The first, the Coarse Predistortion (CPD) method, partially mitigates distortion. The second, the All Predistortion (APD) method, measures the transfer function and significantly enhances exchange oscillation uniformity. Both methods use exchange oscillation homogeneity as the metric and are suitable for any qubit driven by a diabatic pulse. We believe these methods will enhance qubit characterization accuracy and operation quality in future applications.

Solid/liquid hybrid lubrication behaviors of amorphous carbon film coupling with nonpolar and polar base oils

The amorphous carbon film (a-C) has aroused intensive interest in solid-oil hybrid lubrication design due to its low friction, high wear resistance, and good chemical inertness. However, the solid/liquid hybrid lubrication behaviors and mechanisms of a-C films when coupled with nonpolar and polar oils of similar viscosity are still insufficiently understood and ambiguous to date. In this study, we compared the lubrication properties of nonpolar paraffin oil and polar polyether oils with different molecular structures when combined with a-C film. The results demonstrated that the lubrication performance of polyether oils coupled with a-C film surpassed that of paraffin oil across various lubrication regimes. Notably, the stable superlubricity (friction coefficient<0.01) was achieved under mixed lubrication regime on the a-C film when coupled with polyethylene glycol (PEG) oil after a prolonged sliding duration. The tribo-induced formation of carbon quantum dots (CQDs) at the steel/a-C friction interface lubricated by PEG oils was firstly observed. The hydroxylation of the counter ball surface and the fabrication of CQDs might jointly contribute to the achievement of the robust superlubricity of the PEG oil/a-C film hybrid lubrication system.

High acid-base tolerance and long storage time lanthanum cerium co-doped carbon quantum dots for Fe3+ detection

In this paper, lanthanum and cerium co-doped carbon quantum dots (LaCe-CQDs) was firstly synthesized by one step hydrothermal method. The obtained LaCe-CQDs shown sable fluorescence properties with pH values from 3 to 9 and after 4 weeks of storage. The average particle size of LaCe-CQDs, with excitation and emission wavelengths of 350 nm and 446 nm, is 3.27 ± 0.12 nm. Selective analysis of various metal ions revealed the sensitivity of LaCe-CQDs towards Fe3+ ions. Within the 0–60 μM, the fluorescence intensity exhibits a strong linear correlation with the concentration of Fe3+. The limit of detection (LOD) was determined to be 0.753 μM. Additionally, the accuracy of LaCe-CQDs were demonstrated in natural water samples. Therefore, LaCe-CQDs are a promising sensor for Fe3+ detection.

Unveiling graphite anodic expansion: Insights from electrochemical techniques, mass spectrometry, and kinetic modelling

Anodic expansion of graphite at different pH has been studied by coupling a mass spectrometer to an electrochemical cell. The mass spectrometry technique permits to follow the electrochemical gasification of graphite as well as the reaction products formed from the electrolyte. The current and mass spectrometry signals suggest that the neutral medium is the least aggressive for expansion. In addition, chronoamperometric expansion of graphite at different potentials has been carried out using the neutral medium. This experimental approach permits to get detailed information about the reaction mechanism that produces graphene-oxide based materials. The effect of potential and electrolyte concentration have been studied, and it has been observed that the degree of oxidation of the graphene oxide material obtained can be controlled. In addition, a kinetic model based on a phase-moving boundary has been used to describe the chronoamperometric experiments. Two types of graphene oxide materials have been obtained with the anodic synthesis and have been classified as few-layer graphene oxide (FLGO) and graphene oxide quantum dots (GOQDs). The physicochemical and electrochemical properties of both products have been studied.

Emissive glutathione modified sulphur quantum dots for the sensing of lemon yellow and luminescent hydrogels/films

Lemon yellow (LY) is an azo dye which is widely used as food colorant. The continuous consumption can result in the safety concerns for both human and environmental health. This study describes a new sulphur quantum dot (SQD) based fluorescent sensor, which was facilely prepared with oxidized-glutathione (GSSG) as passivator at mild condition of 75 °C. The obtained sulphur quantum dots (GSSG-SQDs) have a relative quantum yield of 0.25, which is 2–5 times that of most SQDs. GSSG-SQDs were used as a sensor for lemon yellow in the concentration range of 0.10–70 μM and the limit of detection of 60 nM. The application was verified with the real sensing of lemon yellow in the soft drinking and tap water, having the standard recovery from 92.5 % to 105 %. Given the great luminescence and photostability, GSSG-SQDs were used as a filler for the preparation of luminescent films and hydrogels as a promising material for a wide range of applications such as information encryption and bioengineering.

Dual-signal biosensor based on G-quadruplex/hemin DNAzyme and zinc-doped molybdenum disulfide quantum dots for ultrasensitive detection of tumor biomarker

Herein, a dual-mode fluorometric and colorimetric biosensor for Pax-5a gene was developed based on zinc-doped molybdenum disulfide quantum dots (Zn-MoS2 QDs) by coupling exonuclease-assisted recycling amplification and peroxidase-mimic DNAzyme. In the presence of Pax-5a gene, the exonuclease III can cleave the duplexes formed by Pax-5a gene and the hairpin DNA (HP), releasing the output DNA (oDNA). G-rich DNA and magnetic beads (MBs) labeled with capture DNA (cDNA) can hybridize with oDNA to form the MBs-cDNA/oDNA/G-rich DNA sandwich complex. The remaining G-rich DNA in the supernatant through magnetic separation could bind hemin to produce G-quadruplex/hemin peroxidase-mimicking DNAzyme, which catalyzed the oxidization of 3,3'-diaminobenzidine (DAB) by H2O2. The generated brown oxidation product (oxDAB) had a distinct absorption peak at 464 nm and could quench the fluorescence of Zn-MoS2 QDs at 406 nm. The high peroxidase activity of DNAzyme, recycling amplification strategy and magnetic separation technique led to excellent sensitivity and specificity of this detection platform. The detection limits of Pax-5a gene by fluorometric and colorimetric methods were 0.52 pM and 1.12 pM, respectively. Furthermore, this sensing system was successfully applied to Pax-5a gene determination in human serum samples, which had promising potential in biochemical analysis and clinical diagnosis.

Investigation of the chemiluminescence behavior of Ti3C2 MXene quantum dots as a sensing platform for uric acid

The current study explores the application of Ti3C2 MXene quantum dots (MQDs) as a chemiluminescent (CL) probe to determine uric acid (UA) in biological samples. The MQDs sensor was synthesized using ultrasonic-assisted hydrothermal method and characterized through Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, and X-ray diffraction. The presence of MQDs significantly enhances the ultra-weak Fe(II)–S2O82− CL system. Subsequently, quenching of the probe’s CL signal was observed in the presence of UA. Thus, the designed CL sensor offers an excellent analytical capability for determining UA in the 0.15–2.5 µM range, with a limit of detection of 0.093 µM. The method was effectively used to analyze UA in human serum and urine, yielding recovery rates between 94.4 % and 108.3 % with relative standard deviations (RSD) ranging from 1.9 % to 5.9 %.

Optical anisotropy of high-order harmonic generation by strong laser radiation in rectangular graphene quantum dot

Optical anisotropy of high-order harmonic generation by strong laser radiation in rectangular graphene quantum dot

A Sensitive and Quick Fluorescent Sensor for the "Turn-On" Detection and Imaging of Glutathione Based on Sulfur Quantum Dots and MnO2 Nanosheets.

Glutathione (GSH) is one of the most abundant bioethanol antioxidants in living cells. Here, a fluorescent probe based on MnO2 nanosheets and sulfur quantum dots (SQDs) was fabricated. Because of the synergistic effect of IFE and FRET, the fluorescence from SQDs was quenched by MnO2 nanosheets. In the presence of GSH, the fluorescence of SQDs could be recovered because of the reduction of MnO2 nanosheets by GSH. The method can detect GSH in the concentration range of 5 ~ 1000 μM with the detection limit as low as 1.26 μM. This quick, easy, and cost-effective sensor could be used for the quantification of GSH in serum samples and the imaging of GSH in Escherichia coli O157:H7.

An adsorbent of molecularly imprinted polymer incorporating graphene quantum dots to extract and determine bisphenols in soft drinks and milk

A highly selective magnetic composite adsorbent composed of graphene quantum dots (GQDs) and molecularly imprinted polymer (MIP) was fabricated and applied for the extraction and quantification of three bisphenols in soft drink and milk samples. Magnetite nanoparticles incorporated into the MIP enabled the adsorbent to be isolated from the sample solution with a magnet. The extraction efficiency toward target bisphenols was enhanced by the selective recognition sites of the MIP layer and also the abundant adsorption sites in GQDs. In the optimum condition, the composite adsorbent coupled with high-performance liquid chromatography (HPLC) exhibited linearity in the range of 10.0–200.0 µg L−1. The limit of detection was 3.0 µg L−1 while the limit of quantification was 10.0 µg L−1. Applied to determine bisphenols in real samples, the proposed method achieved relative recoveries from 84.3 % to 94.9 % with relative standard deviations (RSDs) of less than 7 %. The proposed method is simple, rapid, efficient and accurate. The adsorbent can be reused for up to four extraction and desorption cycles, thus reducing the cost of analysis.

Utilization of Biodiesel Residue through Efficient Microwave-Assisted Synthesis of Carbon Quantum Dots: A Versatile Nanomaterial for Environmental Remediation

The rapid expansion of the biodiesel industry has substantially increased crude glycerol residue (CG) production, creating sustainability and economic challenges due to surplus glycerol generation. Conventional purification methods are costly and environmentally demanding, necessitating innovative strategies to utilize this residue effectively. This study innovates by exploring the microwave-assisted synthesis of carbon dots (CDs) from CG, exemplifying a shift toward sustainable biodiesel production by transforming the residue into a multifunctional material. CDs exhibited a nanometric spherical morphology of 2.6 ± 0.3 nm diameter verified by HRTEM analysis. The reduction of oxygen confirmed the transformation of CG into CDs–H bands and the formation of polyaromatic structures. The graphitic structures were verified by Raman spectroscopy, electron paramagnetic resonance, and X-ray diffraction. The quantum yield (QY) was calculated to be 1.3%. The multifunctionality of CDs has been proven in sensing and photocatalysis. In the sensor applications, the CDs demonstrated strong fluorescence quenching in the presence of Fe3+ and Cu2+ ions, with a limit of detection of 1.8 ± 0.01 and 4.0 ± 0.04 mg.L-1, respectively, indicating the potential use of CDs in detecting these ions in wastewater samples. When complexed with titanium dioxide (TiO2), the TiO2/CDs composite showed an extended photoresponse of TiO2 to the UV-visible region, improving the efficiency of photocatalytic reactions for Victoria Blue B (VBB) dye degradation (98% degradation after 150 min). This research highlights the potential of utilizing CG to produce versatile CDs, contribute to more sustainable biodiesel production, and offer promising applications in environmental sensing and photocatalysis.

An oriented self-assembly biosensor with built-in error-checking for precise midkine detection in cancer diagnosis and prognosis evaluation

Midkine (MDK) is a neurotrophic growth factor highly expressed during embryogenesis, currently recognized as a multifaceted factor in cancer progression and drug resistance. MDK has demonstrated greater accuracy than existing biomarkers. Serum MDK is a valuable indicator for the non-invasive early detection of tumors. It dynamically changes following surgical tumor excision and prior to recurrence, facilitating prognosis and treatment response evaluation. However, existing methods struggle to achieve the sensitivity required for clinical applications. Herein, we developed a triple-mode biosensor with oriented self-construction and built-in error-checking for rapid, sensitive, and convenient MDK detection. The sensor construction adhered to the principle of achieving oriented and strong covalent connections to ensure high sensitivity. Biosynthesized quantum dots (BQDs) were introduced to orient antibodies, enhancing the exploration of active binding sites and significantly increasing antibody-capturing ability. To further enhance sensitivity and signal amplification, Au@Pt nanorods-Ab2 (MF-Probe) were used as multifunctional probes, incorporating an error-checking mechanism to minimize false results. Detection was feasible using an electrochemical workstation, a microplate reader, and even a mobile phone. The sensor exhibited a wide linear range from 5 fg/mL to 100 ng/mL and a low limit of detection (LOD) of 1.620 fg/mL. It accurately distinguished MDK levels in the serum of healthy donors and cancer patients. Compared to existing ELISA kits, it exhibited a lower LOD and a more sensitive response to trace MDK, suggesting it is a promising tool for cancer diagnosis and prognostic evaluation.

Tribological properties of polyimide coating filled with solvent-free covalent carbon quantum dots nanofluids

Novel organic coatings were developed by incorporating solvent-free covalent carbon quantum dots nanofluids (CQDs NFs) into a polyimide (PI) matrix. The tribological properties of CQDs NFs/PI composite coatings were tested using a ball-on-disk tribometer, revealing that even a low loading of CQDs NFs significantly improved tribological performance of PI. Molecular dynamics (MD) simulations and nanoindentation tests showed that CQDs NFs restricted PI molecular chain movement, enhancing mechanical properties. Additionally, CQDs NFs promoted the formation of stable transfer films on steel surfaces, improving wear resistance. This study confirms CQDs NFs' effectiveness in modifying PI composite coatings' friction and wear properties.

Near-infrared enhanced organic se-doped carbon nitride quantum dots nanozymes as SOD/CAT mimics for anti-Parkinson via ROS-NF-κB-NLRP3 inflammasome axis

Development of effective and innovative approaches by inhibiting chronic microglial neuroinflammationto degrade α-synuclein is urgent for Parkinson’s disease (PD) treatment. Here, organic Se(−2 valence)-doped carbon nitride quantum dots (SegCN-QDs) nanozyme were prepared for selective gas/drug combination therapy of PD. SegCN-QDs nanozyme could load Cordycepin (Cor) to cross the blood–brain barrier (BBB) for visualized targeted regulation of microglia to efficiently scavenge α-synuclein aggregates to treat PD. We revealed that SegCN-QDs could targete microglia through the specific interactions between the V domain of the positively charged advanced glycation end products (RAGE) on the surface of microglia and the negatively charged SegCN-QDs. SegCN-QDs also exhibited a wide absorption band spanning entire visible and even near-infrared (NIR) regions, enabling the promotion of water splitting to generate oxygen through NIR irradiation. In addition, SegCN-QDs showed superoxide dismutase (SOD)/catalase (CAT) mimics enzyme activities, which converted reactive oxygen species (ROS) into O2 to alleviate inflammatory response by inhibiting the ROS-nuclear factor-kappa B (NF-κB)/NOD-like receptor protein 3 (NLRP3) axis at the PD sites. Furthermore, the produced oxygen, scavenged ROS, and the delivered Cor were proved to successfully decrease α-synuclein to mitigate dopaminergic neuron injury in vivo and improved motor dysfunction and exploration ability of MPTP-induced PD mice.

Machine learning framework for selective and sensitive metal ion sensing with nitrogen-doped graphene quantum dots heterostructure

This study introduces a machine learning (ML) framework to optimize photodetector performance for sensor applications. Using the data from the fabricated photodetector with the heterostructure of nitrogen-doped graphene quantum dot and gold nanoparticles (Au@N-GQDs), various supervised ML models (more than 20 models) are trained and tested for the selection and refinement of the most effective algorithm for our work. Depending on the best-performed ML model, the optimized working wavelength of the photodetector is found for the detection of metal ions. Remarkably, the ML-based sensor shows a high level of selectivity and sensitivity in nM level towards Fe3+ ions in Brahmaputra river water. A strong alignment between model predictions and experimental outcomes validates the efficacy of the proposed ML-based framework. Moreover, data visualization techniques such as heatmaps, classification algorithms, and confusion matrices are introduced to identify the trends in the database. The mechanistic insight of the sensor performance towards Fe3+ ion sensing is further explained with heatmap analysis and experimental verification, which emphasizes the role of photo-induced charge transfer and Fe–O bond formation between metal ions and Au@N-GQDs due to the high electron affinity of Fe3+ ions.

Universal control of four singlet-triplet qubits.

The coherent control of interacting spins in semiconductor quantum dots is of strong interest for quantum information processing and for studying quantum magnetism from the bottom up. Here we present a 2 × 4 germanium quantum dot array with full and controllable interactions between nearest-neighbour spins. As a demonstration of the level of control, we define four singlet-triplet qubits in this system and show two-axis single-qubit control of each qubit and SWAP-style two-qubit gates between all neighbouring qubit pairs, yielding average single-qubit gate fidelities of 99.49(8)-99.84(1)% and Bell state fidelities of 73(1)-90(1)%. Combining these operations, we experimentally implement a circuit designed to generate and distribute entanglement across the array. A remote Bell state with a fidelity of 75(2)% and concurrence of 22(4)% is achieved. These results highlight the potential of singlet-triplet qubits as a competing platform for quantum computing and indicate that scaling up the control of quantum dot spins in extended bilinear arrays can be feasible.

Revealing and Manipulating Hidden Fine-Structure Coherence of Bright Excitons in CsPbI3 Perovskite Quantum Dots.

Observation and understanding of fine-structure splitting of bright excitons in lead halide perovskite quantum dots (QDs) are crucial to their emerging applications in quantum light sources and exciton coherence manipulation. Recent studies demonstrate that ensemble-level polarization-resolved transient absorption spectroscopy can reveal the quantum beats arising from the coherence between two fine-structure levels. Here we report the observation of an extra fine-structure quantum coherence hidden in previous studies by using cryo-magnetic quantum beat spectroscopy. In ∼6 nm CsPbI3 QDs, two splitting energies of 0.25 and 1.20 meV were observed at 1.7 K, which gradually increased to 0.74 and 1.55 meV, respectively, when a longitudinal magnetic field up to 7 T was applied. The field dependence allowed us to extract two distinct nominal Landé g-factors corresponding to QDs with different orientations with respect to the external field.

Electrochemical biosensor based on Au5Ir@graphene quantum dot nanocomposite and DNA walker for detection of atrazine in environmental water with extremely high sensitivity and selectivity

Existing electrochemical sensors are inadequate for detecting pesticides at extremely low level. This study presents an electrochemical biosensor based on gold-iridium alloy (Au5Ir) and DNA walker for detection of atrazine. Au5Ir@RFBP-GQD nanocomposite was synthesized via the reduction of chloroauric acid and iridium trichloride using arginine and folic acid-functionalized boron and phosphorus-doped graphene quantum dot (RFBP-GQD). The synergy between Au and Ir, along with the formation of Schottky heterojunction, enhances the catalytic activity. The Au5Ir was covalently conjugated with hairpin DNA and thionine forming a redox probe that was used to construct the electrochemical biosensor for atrazine detection, coupled with a DNA walker mechanism. Atrazine triggers the DNA walker, leading to the introduction of multiple redox probes onto the gold electrode surface. The oxidation and reduction of thionine molecules within these redox probes elicit highly sensitive electrochemical response. The integration of Au5Ir@RFBP-GQD catalysis with the DNA walker results in significant signal amplification. The biosensor exhibits superior sensitivity and selectivity compared to other atrazine sensors, with a linear detection range from 1×10−18 to 1×10−12 M and a low detection limit of 3.4×10−19 M (S/N=3). The proposed analytical method was successfully used for detection of atrazine in environmental water.