Rational Design of Capping Ligands of Quantum Dots for Biosensing

Quantum dots have been widely applied in biosensing due to their outstanding optical properties.The emissions of quantum dots are mainly determined by their composition and size,as described by the Brus’s equation.Somehow,in this case,their emissions are hardly regulated reversibly and responsively,which are unsuitable for biosensing and biodetection.In the last decade,capping ligands have been used for designing biosensors because of their responsive regulation on the photoluminescence of quantum dots.Here,we first summarize the advances in characterization and calculation specific for ligands,which have helped to provide insights into the photoluminescence process and energy band theory of quantum dots.We then review two ways of ligand design that influence the optical properties of quantum dots:affecting the process of photoluminescence,or the orbital/electronic structure.In the latter case,the atoms on both the ligand and the surface of the quantum dot interact to affect the energy band structure of the quantum dot core.Examples are presented of how these quantum dots that possess responsive properties due to the design of the ligands have been applied to sensing.With further exploration,we hope to see advances in the fundamental understanding of the energy band structures and practical applications of these quantum dots.

Recent Advances in Triplet-Triplet Annihilation Upconversion for Bioimaging and Biosensing

Photon upconversion is an anti-Stokes process that converts low-energy photons into high-energy photons.The use of upconversion luminescence can avoid the autofluorescence of biological tissue and realize background-free bioimaging with a high signal-to-noise ratio at a low power density.In addition,the excitation of red or near-infrared light facilitates the reduction of photodamage in biological tissues and subsequent bioimaging of deep tissue features in vivo.Meanwhile,upconversion emission-mediated bio sensing offers both high sensitivity and low detection limits for quantitative analysis of the target substances in complicated biological samples.Due to its high upconversion quantum yield,low excitation power density,and tunable absorption and emission wavelengths,triplet-triplet annihilation upconversion(TTA-UC)has garnered considerable interest for bioimaging and biosensing.This review will introduce the fundamental concepts of TTA-UC,the factors that influence TTA-UC materials,and the methodologies for preparing TTA-UC materials.The important progress of TTA-UC in bioimaging and bio sensing in recent years will also be discussed in detail in vitro and in vivo.Furthermore,the current challenges of TTA-UC in bioimaging and biosensing will be discussed,along with potential solutions.

A robust and unique approach for tuning the energy level of Ag_(2)Se quantum dots via“on-surface”manipulation of nitrogencontaining groups of surface-coordinated ligands

Effects of surface chemistry on energy levels or optical properties of semiconductor nanocrystals have attracted considerable attention and show great promise in broad applications.Yet,it remains challenging to controllably tune the photoluminescence(PL)of quantum dots(QDs)by manipulating surface ligands.Herein,we investigated effects of the ligand,glutathione(GSH),on PL properties of near-infrared(NIR)Ag_(2)Se QDs by“on-surface”manipulation,that is,precisely manipulating the chelating group without dissociating the ligand from the surface.The anchoring of the amino group was found to be controlled by solution pH,whereas the binding of the thiol group to the Ag+was pH independent,maintaining the“on-surface”state of GSH.By tuning the pH-controlled binding of amino groups,the energy level or the bandgap of Ag2Se QDs could be increased by up to 140 meV.The increased bandgap resulted in the blueshift of PL spectrum,which could be reversibly tuned by up to 75 nm.The pH-mediated tunable PL properties of QDs could also be extended to other nitrogen-containing pH-sensitive groups which could coordinate to the Ag+,not limited to the amino group.Our work would facilitate the study of nanocrystal surface chemistry and our model that the binding of amino groups affected energy levels of Ag2Se QDs might facilitate new insights into the electronic structure and energy level of other QD-ligand complexes.

Increase of chiral sensing ability in host-guest chemistry by magnetic anisotropy

Enantiomeric molecules generally play distinct functions in chemistry,biology,and pharmacology.Similar physical and chemical properties of chiral analytes lay difficulty in discrimination and quantification of the enantiomers.We report herein an efficient approach of increasing the chiral sensing ability ofβ-cyclodextrin(β-CD),a widely used host molecule,in the hostguest chemistry by magnetic anisotropy.A rigid and chiral lanthanide binding tag was attached to theβ-CD to amplify the changes of nuclear magnetic resonance(NMR)signals in the host-guest recognition process.The installation of the paramagnetic lanthanide ion inβ-CD greatly enhances the enantiomeric discrimination up to 30-fold in comparison with the diamagneticβ-CD reference.In addition,the magnitude of the paramagnetic effects is tunable according to the diverse range of paramagnetic strength of the lanthanide series.The reported method significantly increases the chiral sensing ability ofβ-CD,which can be applied to other host molecules.The transferred paramagnetic effects,pseudocontact shifts(PCSs)and paramagnetic relaxation enhancements(PREs),from the host to the guest molecules,are valuable structural restraints to determine the absolute stereochemistry of the chiral analytes.The strategy does not need modification of the analytes and is complementary to the reported analytical methods that rely on the functionalization of the chiral analytes.

Intracellular redox potential-driven live-cell synthesis of CdSe quantum dots in Staphylococcus aureus

Biosynthesized semiconductor quantum dots(QDs) have bright fluorescence,adjustable particle sizes,and environmental friendliness,endowing them with convenience and potential for biological applications.Due to the unclear mechanism of the cellular environment on the live-cell synthesis of QDs,it is still difficult to regulate their optical properties.Here,the critical role of the intracellular redox environment in regulating the fluorescence properties of biosynthesized CdSe QDs in Staphylococcus aureus(S.aureus) has been elucidated.The glutathione peroxidase(GPx) activity directly affects the intracellular H_(2)O_(2) produced in the SeO_(3)^(2-) reduction,which further manipulates the glutathione redox cycle to determine the content of low-valence Seintermediates.As a result,the fluorescence intensity of the synthesized CdSe QDs increases by 60% in the GPx overexpressed cells.The cellular redox potential that is controlled by the GSH redox cycle provides the driving force for the reduction of SeO_(3)^(2-),facilitating the synthesis of CdSe QDs in S.aureus cells.The proposed mechanism of the cellular redox state provides a new perspective for regulating the synthesis of semiconductor nanomaterials in live cells.

Thioredoxin pathway regulated live-cell synthesis of CdSe quantum dots in Saccharomyces cerevisiae

Currently, the application of synthetic biology to artificially manipulate and utilize organisms for the synthesis of desired products such as nanomaterials with excellent fluorescence properties is attracting considerable attention. However, it is still difficult to obtain designed products efficiently due to insufficient knowledge of the biosynthetic mechanisms. The thioredoxin(TRX) and glutathione(GSH) pathways are generally conserved thiol-reductase systems that protect organisms from oxidative stress and are involved in selenium(Se) metabolism. In this study, we revealed the pivotal role of cytoplasmic TRX pathway in regulating the metabolism of Na_(2)SeO_(3) during the live-cell synthesis of cadmium-selenium quantum dots(Cd Se QDs) in Saccharomyces cerevisiae by regulating the expression level of genes related to TRX pathway and measuring the intracellular content of selenocysteine(Se Cys). The determination of Se Cys metabolism in yeast with GSH pathway-related genes deleted demonstrated that the TRX pathway played a more significant role in Se Cys metabolism than GSH pathway. A 6.4-fold enhancement in the synthetic yield of Cd Se QDs was achieved through the overexpression of TRX pathway-related genes,improvement of synthetic procedure, and supplementation of GSH based on the understanding of biological metabolism.Exploring the mechanism of CdSe QDs live-cell synthesis facilitates the precise manipulation of biological processes for the synthesis of inorganic nanomaterials.

Mass Spectrometry-based Deep Coverage Proteome:Evaluation of Cellular Protein Extraction Methods

The current study comprehensively evaluates four different protein extraction methods based on urea,sodium dodecyl sulfate(SDS),anionic surfactants(BT),and total RNA extractor(Trizol),aiming to optimize the sample preparation workflow for mass spectrometry-based proteomics.Using HeLa cells as an example,we found that the method employing the mass spectrometry-compatible surfactant BT reagent significantly reduces the total time consumed for protein extraction and minimizes protein losses during the sample preparation process.Further integrating the four protein extraction methods,we identified over 7000 proteins from HeLa cells without relying on pre-fractionation techniques,and 2990 of them were quantified using label-free quantification.It is worth noting that the BT and SDS methods demonstrate higher efficiency in extracting membrane proteins,while the Urea and Trizol methods are more effective in extracting proteins from nuclear and cytoplasmic fractions.In summary,this study provides a novel solution for deep proteome coverage,particularly in the context of cellular protein extraction,by integrating mass spectrometry-compatible surfactants with traditional extraction methods to effectively enhance protein identification numbers.

Quantification of albumin in urine using preconcentration and near-infrared diffuse reflectance spectroscopy

Urinary albumin is an important diagnostic and prognostic marker for cardiorenal disease, Recent studies have shown that elevation of albumin excretion even in normal concentration range is associated with increased cardiorenal risk. Therefore, accurate measurement of urinary albumin in normal concentration range is necessary for clinical diagnosis. In this work, thiourea-functionalized silica nanoparticles are prepared and used for preconcentration of albumin in urine. The adsorbent with the analyte was then used for near-infrared diffuse reflectance spectroscopy measurement directly and partial least squares model was established for quantitative prediction. Forty samples were taken as calibration set for establishing PLS model and 17 samples were used for validation of the method. The correlation coefficient and the root mean squared error of cross validation is 0.9986 and 0.43, respectively. Residual predictive deviation value of the model is as high as 18.8. The recoveries of the 17 validation samples in the concentration range of 3.39-24.39 mg/L are between 95.9%-113.1%. Therefore. the method may urovide a candidate method to auantifv albumin excretion in urine_

Understanding the thermal stability of human serum proteins with the related near-infrared spectral variables selected by Monte Carlo-uninformative variable elimination

Understanding the thermal stability of the proteins in human serum is essential since human serum is the important source of pharmaceutical proteins. Near-infrared（NIR） spectroscopy was applied to the investigation of thermal changes in secondary structure and hydration of human serum proteins.However, as a multicomponent system, the overlap of the broad NIR bands makes the structural analysis very difficult directly using the spectra of serum samples. Therefore, continuous wavelet transform（CWT） was used to improve the resolution of NIR spectra, and Monte Carlo-uninformative variable elimination（MC-UVE） method was applied to the selection of the variables associated with the proteins for the structural analysis. The variables（5956, 5867, 5815, 5747, 4525, 4401, 4359 and 4328 cm^-1） related to protein secondary structures and those（7074, 6951, 6827 and 6700 cm 1） connected with water species were selected. Then, the thermal stability was analyzed through the intensity variations of the selected variables with temperature from 30℃ to 80 ℃. It was found that the variation of the spectral variables related to both a-helix and b-sheet changes apparently around 60 ℃, indicating the beginning of the thermal denaturation and the transition from a-helix to b-sheet. Moreover, an obvious change was found around 60℃for the content of the water specie S3, i.e., the water cluster containing three hydrogen bonds. The result demonstrates that MC-UVE can identify the protein-related NIR spectral variables, and the water species may be a marker for investigation of the structural change of proteins in biochemical systems.

Near-infrared spectroscopy and chemometric modelling for rapid diagnosis of kidney disease

Rapid diagnosis is important for efficient treatment in clinical medicine.This study aimed at development of a method for rapid and reliable diagnosis using near-infrared(NIR)spectra of human serum samples with the help of chemometric modelling.The NIR spectra of sera from 48 healthy individuals and 16 patients with suspected kidney disease were analyzed.Discrete wavelet transform(DWT)and variable selection were adopted to extract the useful information from the spectra.Principal component analysis(PCA),linear discriminant analysis(LDA)and partial least squares discriminant analysis(PLSDA)were used for discrimination of the samples.Classification of the two-class sera was obtained using LDA and PLSDA with the help of DWT and variable selection.DWT-LDA produced 93.8%and 83.3%of the recognition rates for the validation samples of the two classes,and 100%recognition rates were obtained using DWT-PLSDA.The results demonstrated that the tiny differences between the spectra of the sera were effectively explored using DWT and variable selection,and the differences can be used for discrimination of the sera from healthy and possible patients.NIR spectroscopy and chemometrics may be a potential technique for fast diagnosis of kidney disease.

Programmable and Reversible Regulation of Catalytic Hemin@MOFs Activities with DNA Structures

Metal-organic frameworks(MOFs)-based nanozyme plays an important role in biosensing,therapy and catalysis.In this study,the effects of single-stranded DNA(ssDNA)with programmable sequences and its complementary DNA(Tdna)on the intrinsic peroxidase-like activity of hemin loaded MOFs(UiO-66-NH2),denoted as he-min@UiO-66-NH2,were investigated.The hemin@UiO-66-NH2 exhibited improved catalytic activity compared with free hemin.However,the catalytic activity is inhibited in the presence of ssDNA,as ssDNA can be adsorbed by MOFs and therefore protected the active sites from contact with substrates.Upon the addition of the TDNA,double-stranded DNA(dsDNA)was formed and detached from the MOFs,resulting in the recovery of catalytic activity.Sequentially adding ssDNA or its complementary DNA strands can achieve the reversible regulation of the catalytic activity of MOFs nanozymes.Moreover,the DNA hybridization-based regulation was further applied to a cascaded catalytic system composed of the nanozyme,hemin@UiO-66-NH2,and glucose oxidase.These nanozyme based programmable and reversibly regulated catalytic systems may have potential applications in future smart biosensing and catalysis systems.

Curved carbon photo-oxygenation catalysts for the suppression and nanoscopic imaging ofβ-amyloid peptides fibrillation

The progression of Alzheimer’s disease(AD)is characterized with the deposition and aggregation ofβ-amyloid(Aβ).Visualizing Aβaggregates at high spatial resolution is beneficial for AD diagnosis and treatment.Herein,we designed a new molecule by conjugating corannulene(Cor)with rhodamine B isothiocyanate(Rhb),namely Cor-Rhb,for the nanoscopic imaging and modulating Aβpeptide fibrillation.The low duty cycle,high photon output and sufficient switching cycles enable Cor-Rhb suitable for localization-based nanoscopic fluorescence imaging.We find that Cor-Rhb can inhibit Aβpeptides fibrillization and interact directly with mature fibrils,triggering their disaggregation under light illumination.Noticeably reduced Aβ-mediated cytotoxicity after the addition of Cor-Rhb is also confirmed.These explorations suggest that Cor-Rhb displays great potential as a multifunctional therapeutic agent against amyloid-related diseases,and may largely facilitate a variety of super-resolution based biological applications.

Ultra-bright near-infrared-IIb emitting Zn-doped Ag_(2)Te quantum dots for noninvasive monitoring of traumatic brain injury

The long-wavelength region of the near-infrared-IIb(NIR-IIb,1,500–1,700 nm)imaging window has become an ideal window for in vivo imaging due to the suppressed photon scattering and near-zero autofluorescence of biological tissues.Therefore,it is necessary to develop fluorescent probes with excellent fluorescence performance and stability for NIR-IIb fluorescence imaging.In this work,zinc-doped silver telluride quantum dots(Zn:Ag_(2)Te QDs)with bright fluorescence in the NIR-IIb window were synthesized.The introduction of Zn dopants inhibited crystal defects and reduced non-radiative transitions.Therefore,the quantum yield and fluorescence lifetime of Zn:Ag_(2)Te QDs were significantly improved.In addition,Zn-doping increased the number of ligands on the surface of QDs,thus enhancing the colloidal stability of Zn:Ag_(2)Te QDs.Moreover,the PEGylated Zn:Ag_(2)Te QDs with high absolute quantum yield realized noninvasive imaging of cerebral vascular of mouse with high resolution able to distinguish blood capillary,which could be utilized to monitor the brain condition of mice after traumatic brain injury.

Overriding the inherent alkalinity to dual phosphinito bimetallic catalyst for C(sp^(2))-C(sp^(3))formation:A combined computational and experimental study

Unraveling the catalytic reaction mechanism is a long-term challenge for developing efficient catalysts.The blooming bimetallic catalyst have enabled to activate inert bonds and realize complex C-C formation.Herein,we theoretically discover a dual-phosphinito bridged hetero-bimetallic species that verified by NMR experiments.Our results indicate only dual-phosphinito Ni-Al model can be an active catalyst in asymmetric cycloadditions via C-C activation and C-H activation,which can well rationalize the experimental observations for both reactivity and stereo-selectivity.An unprecedented tandem redox dehydrogenation mechanism was revealed to control the formation of this active species overriding the inherent basicity.Synergistic Lewis acid and eg orbital interactions,including dz2 orbital reoccupation and d_(x^(2)−y^(2))orbital recombination,were disclosed to understand both thermodynamic and kinetic advance of dual-bridged model,displaying feasible redox properties.

Iron-Catalyzed Cross-Electrophile Coupling of Inert C-O Bonds with Alkyl Bromides

An example of iron-catalyzed cross-electrophile couplingof inert C-O bonds with alkyl bromides via aniron/B_(2)pin_(2) catalytic system has been developed.Aryl and heteroaryl carbamates can smoothly undergothis transformation under mild conditions, deliveringthe alkylated products with good efficiency.This protocol exhibits good functional group compatibilityand enables the late-stage functionalizationof biorelevant compounds, thus providingexcellent opportunities for applications in medicinalchemistry. Control experiments and computationalstudies reveal that a high spin Fe(I/II/III) catalyticmechanism might be involved in this reactionthrough single electron transfer to activate alkylbromides, oxidative addition of aryl carbamates, andreductive elimination to form Csp^(2)-Csp^(3) bonds.

利用定量单病毒示踪技术探究SARS-CoV-2与细胞膜融合动态过程

Viral envelope fusion with the host plasma membrane(PM)for genome release is a hallmark step in the life cycle of many enveloped viruses.This process is regulated by a complex network of biomolecules on the PM,but robust tools to precisely elucidate the dynamic mechanisms of virus-PM fusion events are still lacking.Here,we developed a quantitative single-virus tracking approach based on highly efficient dual-color labelling of viruses and batch trajectory analysis to achieve the spatiotemporal quantification of fusion events.This approach allows us to comprehensively analyze the membrane fusion mechanism utilized by pseudotyped severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)at the singlevirus level and precisely elucidate how the relevant biomolecules synergistically regulate the fusion process.Our results revealed that SARS-CoV-2 may promote the formation of supersaturated clusters of cholesterol to facilitate the initiation of the membrane fusion process and accelerate the viral genome release.

Titanium dioxide as an adsorbent to enhance the detection ability of near-infrared diffuse reflectance spectroscopy

A method for quantitative determination of fish sperm deoxyribonucleic acid(fsDNA)was developed by using titanium dioxide(TiO2)as an adsorbent and near-infrared diffuse reflectance spectroscopy(NIRDRS).The selective enrichment of fsDNA was proved by comparing the adsorption efficiency of bovine serum albumin,tyrosine and tryptophan,and the low adsorption background of TiO2 was illustrated by comparing the spectra of four commonly-used inorganic adsorbents(alkaline aluminium oxide,neutral aluminium oxide,nano-hydroxyapatite and silica).The spectral feature of fsDNA can be clearly observed in the spectrum of the sample.Partial least squares(PLS)model was built for quantitative determination of fsDNA using 28 solutions,and 13 solutions with interferences were used for validation of the model.The results showed that the correlation coefficient(R)between the predicted and the reference concentration is 0.9727 and the recoveries of the validation samples are in the range of 98.2%-100.7%.

Designer cell-self-implemented labeling of microvesicles in situ with the intracellular-synthesized quantum dots

Cell-derived microvesicles(MVs) are secreted from almost all kinds of mammalian cells into the extracellular space, and play crucial roles in intercellular communication and transporting biomolecules between cells. However, there is a great challenge for visualizing and monitoring of MVs’ bio-behaviors due to the limitations of existing labeling methods. Herein, we report the first paradigm of designer cell-self-implemented labeling of MVs secreted from living mammalian MCF-7 cells in situ using the intracellular-synthesized fluorescent quantum dots(QDs) during the formation of MVs. By elaborately coupling intracellular biochemical reactions and metabolism pathways, the MCF-7 cells can be illuminated brightly by intracellular-biosynthesized fluorescent CdSe QDs. Simultaneously, intracellular-synthesized QDs can be in situ encapsulated by the secreted MVs budding from the plasma membrane of the fluorescing cells to label the MVs with an efficiency of up to 89.9%. The whole labeling process skillfully combines designer precise cell-tuned intricate synthesis of CdSe QDs with mild in-situ labeling via cell-selfimplementation just after feeding the cell with suitable chemicals, which is structure-or function-nondestructive and much more straightforward and milder than those by chemical conjugation or indirect encapsulation with conventional fluorogenic labels.

Determination of triglycerides in human serum by near-infrared diffuse reflectance spectroscopy using silver mirror as a substrate

Near infrared diffuse reflectance spectroscopy(NIRDRS) has gained wide attention due to its convenience for rapid quantitative analysis of complex samples. A method for rapid analysis of triglycerides in human serum using NIRDRS with silver mirror as the substrate is developed. Due to the even and high reflectance of the silver mirror, the spectral response is enhanced and the background interference is reduced.Furthermore, both linear and nonlinear modeling strategies were investigated adopting the partial least squares(PLS) and least squares support vector regression(LS-SVR), continuous wavelet transform(CWT)was used for spectral preprocessing, and variable selection was tried using Monte Carlo uninformative variable elimination(MC-UVE), randomization test(RT) and competitive adaptive reweighted sampling(CARS) for optimization the models. The results show that the determination coefficient(R) between the predicted and reference concentration is 0.9624 and the root mean squared error of prediction(RMSEP) is 0.21. The maximum deviation of the prediction results is as low as 0.473 mmol/L. The proposed method may provide an alternative method for routine analysis of serum triglycerides in clinical applications.

Blinking CsPbBr_(3) perovskite nanocrystals for the nanoscopic imaging of electrospun nanofibers

Blinking fluorophore perovskite nanocrystals (NCs) were employed to image the fine structure of the polystyrene (PS) electrospun fibers. The conditions of CsPbBr3 NCs embedded and dispersed into PS were investigated and optimized. The stochastic optical reconstruction microscopy is employed to visualize the fine structure of the resulted CsPbBr3@PS electrospun fibers at sub-diffraction limit. The determined resolution in the reconstructed nanoscopic image is around 25.5 nm, which is much narrower than that of conventional fluorescence image. The complex reticulation and multicompartment in bead sub-diffraction-limited structures of CsPbBr3@PS electrospun fibers were successfully mapped with the help of the stochastic blinking properties of CsPbBr3 NCs. This work demonstrated the potential applications of CsPbBr3 perovskite NCs in super-resolution fluorescence imaging to reconstruct the sub-diffraction-limited features of polymeric material.