Quantum Dot Nanoprobes Research Articles

Fluorescent and colorimetric dual-readout platform for tuberculosis point-of-care detection based on dual signal amplification strategy and quantum dot nanoprobe

Rapid and accurate diagnosis of tuberculosis (TB) is of great significance to control the spread of this devastating infectious disease. In this work, a sensitive and low-cost point-of-care testing (POCT) detection platform for TB was developed based on recombinase polymerase amplification (RPA)-catalytic hairpin assembly (CHA)-assisted dual signal amplification strategy. This platform could achieve homogeneous fluorescent and visual diagnosis of TB by using CdTe quantum dots (QDs) signal reporter. In the presence of target DNA (IS1081 gene fragment), RPA amplicons blocked by short oligonucleotide strands could trigger CHA signal amplification, leading to the Ag+ releasing from C–Ag+-C structure and the fluorescence quenching of CdTe QDs by the released Ag+. Furthermore, the detection performance of CdTe QDs modified by 3-mercaptopropionic acid (MPA) or thiomalic acid (TMA) (MPA-capped QDs and TMA-capped QDs) was systematically compared. Experimental results demonstrated that TMA-capped QDs exhibited better detection sensitivity due to their stronger interaction with Ag+. The limits of detection (LODs) of fluorescence and visual analysis were as low as 0.13 amol L−1 and 0.33 amol L−1. This method was successfully applied to the clinical sputum samples from 36 TB patients and 20 healthy individuals, and its quantitative results were highly consistent with those obtained by real-time fluorescent quantitative polymerase chain reaction (RT-qPCR). The proposed approach has the advantages of high sensitivity and specificity, simple operation and low cost, and is expected to be applied in clinical TB screening and diagnosis.

Mango Leaves (Mangifera indica)-Derived Highly Florescent Green Graphene Quantum Dot Nanoprobes for Enhanced On-Off Dual Detection of Cholesterol and Fe2+ Ions Based on Molecular Logic Operation.

In the present study, we have engineered a molecular logic gate system employing both Fe2+ ions and cholesterol as bioanalytes for innovative detection strategies. We utilized a green-synthesis method employing the mango leaves extract to create fluorescent graphene quantum dots termed "mGQDs". Through techniques like HR-TEM, i.e., high-resolution transmission electron microscopy, Raman spectroscopy, and XPS, i.e., X-ray photoelectron spectroscopy, the successful formation of mGQDs was confirmed. The photoluminescence (PL) characteristics of mGQDs were investigated for potential applications in metal ion detection, specifically Fe2+ traces in water, by using fluorescence techniques. Under 425 nm excitation, mGQDs exhibited emission bands at 495 and 677 nm in their PL spectrum. Fe2+-induced notable quenching of mGQDs' PL intensity decreased by 97% with 2.5 μM Fe2+ ions; however, adding 20 mM cholesterol resulted in a 92% recovery. Detection limits were established through a linear Stern-Volmer (S-V) plot at room temperature, yielding values of 4.07 μM for Fe2+ ions and 1.8 mM for cholesterol. Moreover, mGQDs demonstrated biocompatibility, aqueous solubility, and nontoxicity, facilitating the creation of a rapid nonenzymatic cholesterol detection method. Selectivity and detection studies underscored mGQDs' reliability in cholesterol level monitoring. Additionally, a molecular logic gate system employing Fe2+ metal ions and cholesterol as a bioanalyte was established for detection purposes. Overall, this research introduces an ecofriendly approach to craft mGQDs and highlights their effectiveness in detecting metal ions and cholesterol, suggesting their potential as versatile nanomaterials for diverse analytical and biomedical applications.

Incorporation of eggshell waste in the preparation of carbon quantum dot nanoprobes for the determination of COVID-19 antiviral drug; molnupiravir

New carbon quantum dots (CQDs) with multi-doped elements from eggshell biomass waste have been employed as a direct, fast, green, and selective probe for the fluorometric determination of molnupiravir, a COVID-19 antiviral drug. For the first time, the eggshell@CQDs were prepared through a simple, single-step microwave heating process that only took 90 s. Upon excitation at λex 340 nm, the resulting CQDs exhibited a maximum bluish fluorescence emission at λem 408 nm. Molnupiravir was found to quench the native fluorescence of the prepared CQDs in a quantitative manner, based on a static mechanism by forming a non-emissive complex. The spectrofluorometric method designed for molnupiravir detection was validated per the International Council for Harmonization (ICH) requirements. The proposed fluorescent probe showed good linearity for molnupiravir detection over a range of 2.5–70 µg/mL, with percent recoveries ranging from 99.53 % to 101.79 % and %RSD (relative standard deviation) less than 1 %. The eggshell@CQDs were successfully employed to determine molnupiravir levels in marketed hard capsules, yielding good percent recoveries and repeatability. The developed approach was found to be greener than the published HPLC/UV approach, as assessed by the analytical eco-scale, green analytical procedure index (GAPI), and analytical greenness metric approach (AGREE). Furthermore, this approach highlights the potential of synthesizing CQDs from natural biomass, specifically low-value biomass waste such as eggshells.

Amyloid β interferes with wound healing of brain microvascular endothelial cells by disorganizing the actin cytoskeleton

Cerebral amyloid angiopathy (CAA) is a disease in which amyloid β (Aβ) is deposited in the cerebral blood vessels, reducing compliance, tearing and weakening of vessel walls, leading to cerebral hemorrhage. The mechanisms by which Aβ leads to focal wall fragmentation and intimal damage are not well understood. We analyzed the motility of human brain microvascular endothelial cells (hBMECs) in real-time using a wound-healing assay. We observed the suppression of cell migration by visualizing Aβ aggregation using quantum dot (QD) nanoprobes. In addition, using QD nanoprobes and a SiR-actin probe, we simultaneously observed Aβ aggregation and F-actin organization in real-time for the first time. Aβ began to aggregate at the edge of endothelial cells, reducing cell motility. In addition, Aβ aggregation disorganized the actin cytoskeleton and induced abnormal actin aggregation. Aβ aggregated actively in the anterior group, where cell motility was active. Our findings may be a first step toward explaining the mechanism by which Aβ causes vascular wall fragility, bleeding, and rebleeding in CAA.

Wavelength-dependent three-dimensional single-molecule superlocalization imaging for yoctomole detection of thyroid-stimulating hormone on a quantum dot nanobiosensor

A wavelength-dependent three-dimensional (3D) superlocalization imaging method on gold nanoislands (GNIs) chip was developed as a supersensitive single-molecule thyroid-stimulating hormone (TSH) nanobiosensor. Scattered and fluorescent signals from gold nanoislands on the substrate and quantum dots (QDs) nanoprobes were simultaneously isolated and acquired within an evanescent field layer generated by total internal reflection (TIR) of incident light using a dual-view device. The 3D TIR fluorescence images of TSH-bound QDs on the GNIs were obtained using z-axis optical sectioning at 10 nm intervals before/after immunoreaction to identify the optimal conditions for detection. The localized centroid position of QD nanoprobes and GNI were distinguished at a subdiffraction limit resolution using 3D Gaussian fitting to the point spread function. The QD TSH nanobiosensor using wavelength-dependent 3D TIR fluorescence-based single-molecule localization microscopy (3D TIRF-SLM) imaging technique showed an excellent detection limit of 90 yoctomoles (∼54 molecules) and a wide linear dynamic range of 1.14 zmol/L − 100 pmol/L for TSH. The detection sensitivity was about 4.4 × 109 times higher than conventional enzyme-linked immunosorbent assay and could successfully quantify TSH in human serum. The wavelength-dependent 3D TIRF-SLM technique may emerge as a reliable platform for ultrahigh-sensitive nanobiosensors at the single-molecule level and early diagnosis with quantification of disease-related ultra-trace biomolecules.

Synthesis of near-infrared zinc-induced manganese-doped Cu-In-Se quantum dots and their photoluminescence mechanism

Manganese ion-doped quantum dots (QDs) with wide band gaps have been widely investigated to modify their electronic, magnetic, and photophysical properties. The research on Mn-doped Cu-In-Se QDs with narrow band gaps has been minimal due to the profound differences in the reaction reactivity of cations. In this work, photoluminescent and magnetic Cu-In-Se QD nanoprobes were designed and synthesized by introducing Zn2+ ions, which function as an intermediate acid that can regulate metal ion acidity to enhance the doping efficiency of Mn2+ ions in a facile phosphine-free hot-injection protocol. The emission peaks of Zn-doped Cu-In-Se QDs and MnZn-doped Cu-In-Se QDs exhibit significant composition-dependent shifts. Moreover, incorporating manganese ions confers a paramagnetic character to MnZn-doped Cu-In-Se QDs and provides a quasi-core shell structure with an Mn-rich alloy shell layer, as demonstrated by the micro-structural surface analysis and electron paramagnetic resonance spectroscopy. Analyzing the decay lifetime and quantum yield reveals that this host-dopant coupling involves a preferential energy transfer from the host material to the dopant (Mn2+ ions), wherein photogenerated electrons nonradiatively transfer to the 4T1 level of Mn dopant and then recombine with the Cux state above the valance band of host QDs. The ability to serve as nanoprobes for the visualization of tumors through fluorescence and magnetic resonance dual-modality imaging makes these ternary MnZn-doped Cu-In-Se QDs strong candidates for practical applications in biology/biomedicine field.

Cultivation Factors That Affect Amyloid-β Aggregation Inhibitory Activity in Perilla frutescens var. crispa.

Alzheimer's disease (AD) is thought to be caused by the deposition of amyloid-β (Aβ) in the brain. Aβ begins to aggregate approximately 20 years before the expression of its symptoms. Previously, we developed a microliter-scale high-throughput screening (MSHTS) system for inhibitors against Aβ aggregation using quantum dot nanoprobes. Using this system, we also found that plants in the Lamiaceae, particularly Perilla frutescens var. crispa, have high activity. The cultivation environment has the potential to enhance Aβ aggregation inhibitory activity in plants by changing their metabolism. Here, we report on cultivation factors that affected the activity of P. frutescens var. crispa cultivated in three fields under different cultivation conditions. The results revealed that the activity of P. frutescens var. crispa harvested just before flowering was highest. Interestingly, the activity of wind-shielded plants that were cultivated to prevent exposure to wind, was reduced to 1/5th of plants just before flowering. Furthermore, activity just before flowering increased following appropriate nitrogen fertilization and at least one week of drying from the day before harvest. In addition, we confirmed that the P. frutescens var. crispa leaf extracts suppressed Aβ-induced toxicity in nerve growth factor-differentiated PC12 cells. In this study, we demonstrated that flowering, wind, soil water content, and soil nitrogen content affected Aβ aggregation inhibitory activity, necessary to suppress Aβ neurotoxicity, in P. frutescens var. crispa extracts. This study provides practical cultivation methods for P. frutescens var. crispa with high Aβ aggregation inhibitory activity for the prevention of AD.

Y3+@CdTe quantum dot nanoprobe as a fluorescence signal enhancement sensing platform for the visualization of norfloxacin.

Quinolone antibiotics (norfloxacin) pose a serious threat to animal and human health due to their misuse and difficulty in being broken down in surface water and food. Rapid and effective detection of norfloxacin (NOR) is essential for environmental testing and ecosystems. In this study, yttrium was coordinated with mercaptopropionic acid (MPA)-modified CdTe quantum dots (QDs) to obtain a novel fluorescence sensor Y3+@CdTe QDs for the sensitive detection of NOR. NOR can bind to Y3+ to form a complex (NOR-Y3+). This complex enhances the luminescence of NOR and blue-shifts to 423 nm. The fluorescence intensity of NOR-Y3+ at 423 nm (I423) gradually increased with increasing NOR concentration; meanwhile, the fluorescence intensity of CdTe QDs at 634 nm (I634) gradually decreased due to aggregation induction. The ratio of I423 to I634 was used for the quantitative determination of NOR. The linear range of the constructed fluorescent probes was from 1.0 to 150.0 μM, with a detection limit of 31.8 nM. CdTe QDs act as a red fluorescent background, and with the addition of NOR, the color of the system transitions from red to purple and finally blue. This method was rapid (immediate) and visual, providing a simple analysis of various actual samples (tap water, lake water, honey, milk and human serum) for NOR.

Fabrication of polyaspartic acid surface-modified highly fluorescent carbon quantum dot nanoprobe for sensing of reduced glutathione in real sample

Fabrication of polyaspartic acid surface-modified highly fluorescent carbon quantum dot nanoprobe for sensing of reduced glutathione in real sample

Highly Bright Silica-Coated InP/ZnS Quantum Dot-Embedded Silica Nanoparticles as Biocompatible Nanoprobes.

Quantum dots (QDs) have outstanding optical properties such as strong fluorescence, excellent photostability, broad absorption spectra, and narrow emission bands, which make them useful for bioimaging. However, cadmium (Cd)-based QDs, which have been widely studied, have potential toxicity problems. Cd-free QDs have also been studied, but their weak photoluminescence (PL) intensity makes their practical use in bioimaging challenging. In this study, Cd-free QD nanoprobes for bioimaging were fabricated by densely embedding multiple indium phosphide/zinc sulfide (InP/ZnS) QDs onto silica templates and coating them with a silica shell. The fabricated silica-coated InP/ZnS QD-embedded silica nanoparticles (SiO2@InP QDs@SiO2 NPs) exhibited hydrophilic properties because of the surface silica shell. The quantum yield (QY), maximum emission peak wavelength, and full-width half-maximum (FWHM) of the final fabricated SiO2@InP QDs@SiO2 NPs were 6.61%, 527.01 nm, and 44.62 nm, respectively. Moreover, the brightness of the particles could be easily controlled by adjusting the amount of InP/ZnS QDs in the SiO2@InP QDs@SiO2 NPs. When SiO2@InP QDs@SiO2 NPs were administered to tumor syngeneic mice, the fluorescence signal was prominently detected in the tumor because of the preferential distribution of the SiO2@InP QDs@SiO2 NPs, demonstrating their applicability in bioimaging with NPs. Thus, SiO2@InP QDs@SiO2 NPs have the potential to successfully replace Cd-based QDs as highly bright and biocompatible fluorescent nanoprobes.

Kinetics of amyloid accumulation in physiological viscosity

Abnormal aggregation and accumulation of misfolded proteins are involved in the development of various forms of amyloidosis. Aggregates that accumulate in organs induce an inflammatory response and cytotoxicity, and lead to organ failure. Although protein accumulation around an affected area in the body is an important stage that is directly linked to the mechanism of pathogenesis, the kinetics of the accumulation of protein that precipitates while assembling is not well understood because 3D tracking of proteins in solution is difficult. Here, we analyzed the process of aggregation and accumulation of amyloid β (Aβ), which causes the development of Alzheimer's disease (AD), by real-time 3D imaging under physiological conditions using a quantum dot nanoprobe that we previously developed. 3D observations demonstrated that Aβ aggregates with a diameter of several μm emerged in phosphate-buffered saline, gathered in a spiral-like step, and exhibited a mesh-like structure. Additionally, we found that the amount and size of aggregates decreased dramatically in 40% glycerol solution, mimicking the viscosity of human blood. We confirmed that fibrils in 40% glycerol exhibited an extremely short and tangled morphology and formed dense aggregates. Furthermore, numerical calculations revealed that several decades are required to fully develop the settling velocity and diameter of Aβ aggregates in physiological conditions. This time span is consistent with the actual symptom progression of AD.

An Approach to the Simultaneous Detection of Multiple Biomarkers for the Early Diagnosis of Liver Cancer Using Quantum Dot Nanoprobes

Abstract Biomarker-based early diagnosis of liver cancer is of high clinical value for reducing the mortality rate. However, it has been challenging to establish early detection methods with a single biomarker such as alpha-fetoprotein (AFP) because of limited diagnostic sensitivity and specificity. Therefore, developing multiplexed biomarker detection assays is crucially important for early diagnosis. Yet, simultaneous detection methods involving three or more biomarkers have been scarce. Here we suggest employing the serological biomarker panel of glypican-3 (GPC3), dickkopf-1 (DKK1), and AFP for liver cancer detection. We present a rapid simultaneous detection approach for the biomarker panel labeled with three fluorescent quantum dot nanoprobes (emission wavelengths at 565 nm, 605 nm, and 655 nm). As a proof-of-concept, simultaneous fluorescence detection of the biomarker panel was demonstrated using mixed reference samples containing human recombinant GPC3, DKK1, and AFP antigens. Our simultaneous detection approach conferred a linear range of 0.625-2.5 ng•mL-1 for the entire biomarker panel, which merits further clinical validation for the simultaneous and accurate determination of the biomarker panel in human serum samples.

Amyloid β aggregation induces human brain microvascular endothelial cell death with abnormal actin organization

Cerebral amyloid angiopathy (CAA) is a disease in which amyloid β (Aβ) is deposited on the walls of blood vessels in the brain, making those walls brittle and causing cerebral hemorrhage. However, the mechanism underlying its onset is not well understood. The aggregation and accumulation of Aβ cause the occlusion and fragility of blood vessels due to endothelial cell damage, breakdown of the blood-brain barrier, and replacement with elements constituting the blood vessel wall. In this study, we observed the effect of Aβ on human primary brain microvascular endothelial cells (hBMECs) in real-time using quantum dot nanoprobes to elucidate the mechanism of vascular weakening by Aβ. It was observed that Aβ began to aggregate around hBMECs after the start of incubation and that the cells were covered with aggregates. Aβ aggregates firmly anchored the cells on the plate surface, and eventually suppressed cell motility and caused cell death. Furthermore, Aβ aggregation induced the organization of abnormal actin, resulting in a significant increase in intracellular actin dots over 10 μm2. These results suggest that the mechanism by which Aβ forms a fragile vessel wall is as follows: Aβ aggregation around vascular endothelial cells anchors them to the substrate, induces abnormal actin organization, and leads to cell death.

Mechanical analysis of oriented cell movement by nanostructure-based biosensors

Due to the numerous diseases caused by apoptosis, the existing methods for detecting early apoptosis are not effective. To explore the effect of nanostructured biosensors on the directional movement of cells, silica@quantum dot-concanavalin A (SiO2@QDs-ConA) nanoprobes were prepared, and cholesterol amperometric biosensors based on carbon nanotubes were constructed by using the layer-by-layer assembly method. The results showed that in the presence of apoptotic cells, a sharp anodic stripping voltammetric signal was obtained, with a peak potential of about −0.7 V, corresponding to the oxidation peak of the cadmium (Cd2+) ion of the combined quantum dot nanoprobe. The signal of apoptotic cells was 3.9 and 15.0 times higher than those of normal cells and no cells, respectively, indicating the detection of apoptotic cells by electrochemical cell sensors in the early stage. Eight hours before the action of the apoptosis-inducing reagent, part of HL-60 cells underwent apoptosis. Sixteen hours after the action of the reagent, the apoptosis of HL-60 cells was obvious, the action time of the apoptosis-inducing reagent increased, the peak current of cadmium ion enrichment and dissolution increased rapidly and the HL-60 cells had obviously undergone apoptosis, indicating that most of the cells had obviously undergone apoptosis at this time, indicating that use of the constructed sensor is feasible for the early detection of apoptotic cells.

Aggregation of Mouse Serum Amyloid A Protein Was Promoted by Amyloid-Enhancing Factors with the More Genetically Homologous Serum Amyloid A

Amyloid A (AA) amyloidosis is a condition in which amyloid fibrils characterized by a linear morphology and a cross-β structure accumulate and are deposited extracellularly in organs, resulting in chronic inflammatory diseases and infections. The incidence of AA amyloidosis is high in humans and several animal species. Serum amyloid A (SAA) is one of the most important precursor amyloid proteins and plays a vital step in AA amyloidosis. Amyloid enhancing factor (AEF) serves as a seed for fibril formation and shortens the onset of AA amyloidosis sharply. In this study, we examined whether AEFs extracted and purified from five animal species (camel, cat, cattle, goat, and mouse) could promote mouse SAA (mSAA) protein aggregation in vitro using quantum-dot (QD) nanoprobes to visualize the aggregation. The results showed that AEFs shortened and promoted mSAA aggregation. In addition, mouse and cat AEFs showed higher mSAA aggregation-promoting activity than the camel, cattle, and goat AEFs. Interestingly, homology analysis of SAA in these five animal species revealed a more similar amino acid sequence homology between mouse and cat than between other animal species. Furthermore, a detailed comparison of amino acid sequences suggested that it was important to mSAA aggregation-promoting activity that the 48th amino acid was a basic residue (Lys) and the 125th amino acid was an acidic residue (Asp or Glu). These data imply that AA amyloidosis exhibits higher transmission activity among animals carrying genetically homologous SAA gene, and may provide a new understanding of the pathogenesis of amyloidosis.

Luminescent Nanomaterials (II).

In this review, we focus on sensing techniques and biological applications of various luminescent nanoparticles including quantum dot (QD), up-conversion nanoparticles (UCNPs) following the previous chapter. Fluorescent phenomena can be regulated or shifted by interaction between biological targets and luminescence probes depending on their distance, which is so-called Fӧrster resonance energy transfer (FRET). QD-based FRET technique, which has been widely applied as a bioanalytical tool, is described. We discuss time-resolved fluorescence (TRF) imaging and flow cytometry technique, using photoluminescent nanoparticles with unique properties for effectively improving selectivity and sensitivity. Based on these techniques, bioanalytical and biomedical application, bioimaging with QD, UCNPs, and Euripium-activated luminescent nanoprobes are covered. Combination of optical property of these luminescent nanoparticles with special functions such as drug delivery, photothermal therapy (PTT), and photodynamic therapy (PDT) is also described.

Dietary Intake of Rosmarinic Acid Increases Serum Inhibitory Activity in Amyloid A Aggregation and Suppresses Deposition in the Organs of Mice.

Serum amyloid A (SAA) is one of the most important precursor amyloid proteins and plays a vital step in AA amyloidosis, although the underlying aggregation mechanism has not been elucidated. Since SAA aggregation is a key step in this pathogenesis, inhibitors are useful to prevent and treat AA amyloidosis, serving as tools to investigate the pathogenic mechanism. In this study, we showed that rosmarinic acid (RA), which is a well-known inhibitor of the aggregation of amyloid β (Aβ), displayed inhibitory activity against SAA aggregation in vitro using a microliter-scale high-throughput screening (MSHTS) system with quantum-dot nanoprobes. Therefore, we evaluated the amyloid aggregation inhibitory activity of blood and the deposition of SAA in organs by feeding mice with Melissa officinalis extract (ME) containing RA as an active substance. Interestingly, the inhibitory activity of ME-fed mice sera for SAA and Aβ aggregation, measured with the MSHTS system, was higher than that of the control group. The amount of amyloid deposition in the organs of ME-fed mice was lower than that in the control group, suggesting that the SAA aggregation inhibitory activity of serum is associated with SAA deposition. These results suggest that dietary intake of RA-containing ME enhanced amyloid aggregation inhibitory activity of blood and suppressed SAA deposition in organs. This study also demonstrated that the MSHTS system could be applied to in vitro screening and to monitor comprehensive activity of metabolized foods adsorbed by blood.

Evaluation of Amyloid β42 Aggregation Inhibitory Activity of Commercial Dressings by A Microliter-Scale High-Throughput Screening System Using Quantum-Dot Nanoprobes.

The aggregation and accumulation of amyloid β (Aβ) in the brain is a trigger of pathogenesis for Alzheimer’s disease. Previously, we developed a microliter-scale high-throughput screening (MSHTS) system for Aβ42 aggregation inhibitors using quantum-dot nanoprobes. The MSHTS system is seldom influenced by contaminants in samples and is able to directly evaluate Aβ42 aggregation inhibitory activity of samples containing various compounds. In this study, to elucidate whether the MSHTS system could be applied to the evaluation of processed foods, we examined Aβ42 aggregation inhibitory activity of salad dressings, including soy sauces. We estimated the 50% effective concentration (EC50) from serial diluted dressings. Interestingly, all 19 commercial dressings tested showed Aβ42 aggregation inhibitory activity. It was suggested that EC50 differed by as much as 100 times between the dressings with the most (0.065 ± 0.020 v/v%) and least (6.737 ± 5.054 v/v%) inhibitory activity. The highest activity sample is traditional Japanese dressing, soy sauce. It is known that soy sauce is roughly classified into a heat-treated variety and a non-heat-treated variety. We demonstrated that non-heat-treated raw soy sauce exhibited higher Aβ42 aggregation inhibitory activity than heat-treated soy sauce. Herein, we propose that MSHTS system can be applied to processed foods.

SiRNA-directed self-assembled quantum dot biosensor for simultaneous detection of multiple microRNAs at the single-particle level

MicroRNAs are essential post-transcriptional regulators and may act as the noninvasive biomarkers for disease diagnosis. Sensitive and multiplexed detection of microRNAs may facilitate the accurate and early clinical diagnosis, but the available methods are usually compromised by using organic dyes as the signal probes, laborious chemical and enzymatic manipulations, and the complicated reaction schemes. Here we reported a siRNA-directed self-assembled quantum dot (QD) biosensor for facile and simultaneous detection of multiple microRNAs. In this biosensor, the binding of microRNA targets with corresponding QD nanoprobes leads to the formation of siRNA duplexes, which not only induces the spectrally resolved coding of microRNAs, but also facilitates the assembly of QDs:magnetic nanoparticle bioconjugates for the isolation and enrichment of target microRNAs. The disassembled QDs can be sensitively detected by single-molecule detection, enabling quantitatively sensing of microRNAs at the single-particle level. This biosensor employs only QDs as the signal reporters, which can simultaneously detect multiple microRNAs from the same sample and achieves femtomolar sensitivity and single-base mismatch selectivity without the involvement of any target labeling and amplification steps. Moreover, it can be successfully applied for simultaneous detection of circulating microRNAs in clinical serum samples, holding great potential in non-invasive early diagnosis and biomedical researches.

PH-Sensitive Visible or Shortwave Infrared Quantum Dot Nanoprobes Using Conformation-Switchable Copolymeric Ligands

Intracellular and extracellular pH are key parameters in many physiological processes and diseases. For example, the extracellular pH of the tumor micro-environment is slightly more acidic than in healthy tissue. In vivo mapping of the extracellular pH within the tumor would therefore improve our understanding of the tumor physiology. Fluorescent semiconductor quantum dots (QDs) represent interesting probes for in vivo imaging, in particular in the shortwave infrared (SWIR) range. Here, pH-sensitive QD nanoprobes are developed using a conformation-switchable surface chemistry. The central fluorescent QD is coated with a copolymer ligand and conjugated to gold nanoparticle quenchers. As the pH decreases from physiological (7.5) to slightly acidic (5.5-6), the copolymer reversibly shrinks, which increases the energy transfer between the QD and the gold quenchers and modulates the QD fluorescence signal. This enables the design of ratiometric QD probes for biological pH range emitting in the visible or SWIR range. In addition, these probes can be easily encapsulated and remain functional within ghost erythrocyte membranes, which facilitate their in vivo application.