Room temperature synthesis of pH-switchable polyaniline quantum dots as a turn-on fluorescent probe for acidic biotarget labeling

Uniform blue emitting carbon nanodots synthesized from fig fruit using reverse diffusion purification

In this investigation, blue-emitting carbon nanodots (B.CNDs) with exceptional color purity were successfully synthesized from fresh fig fruit using a one-step pyrolysis method. These B.CNDs are small and spherical (3.7 nm) with an amorphous carbon core encapsulated inside a passivated layer primarily composed of oxygen-related functional groups. They demonstrated an emission property that is independent of excitation, showing the highest emission intensity in the deep blue region at 450 nm with a narrow full-width at half maximum (FWHM) at 44 nm and a quantum yield of 15.5%. This exceptional value of FWHM is attributed to the remarkable uniformity in both morphological and chemical composition that was achieved through the utilization of the reverse diffusion technique combined with the dialysis method for purification and separation of B.CNDs. This work not only contributes to the expanding field of carbon nanomaterials but also introduces a novel and sustainable approach to fabricate CDs with unparalleled color purity and optical performance.

Gram-Scale Room-Temperature Synthesis of Solid-State Fluorescent Carbon Nanodots for Bright Electroluminescent Light Emitting Diodes

The reaction conditions of high temperature and high pressure will introduce structural defects, high energy consumption, and security risks, severely hindering the industrial application of organic carbon nanodots (CDs). Moreover, the aggregation caused quenching effect also fundamentally limits the CDs based electroluminescent light emitting diodes (LEDs). Herein, for the first time, a rapid one-step room temperature synthetic strategy is introduced to prepare highly emissive solid-state-fluorescent CDs (RT-CDs). A strong oxidizing agent, potassium periodate (KIO₄ ), is adopted as a catalyst to facilitate the cyclization of o-phenylenediamine and 4-dimethylamino phenol in aqueous solution at room temperature for only 5 min. The resultant organic molecule, 2-(dimethylamino) phenazine, will self-assemble kinetically to generate supramolecular-structure CDs during crystallization. The elaborately arranged supramolecular structure (J aggregates) endows CDs with intense solid-state-fluorescence. Density functional theory (DFT) calculation shows that the excited state of RT-CDs exhibits charge transfer characteristic owing to the unique donor-Π-acceptor structure. A high-performance monochrome RT-CDs based electroluminescent LEDs (2967 cd m^-2 and 1.38 cd A^-1 ) were fabricated via systematic optimizations of device engineering. This work provides a concrete and feasible avenue for the rapid and massive preparation of CDs, advancing the commercialization of CDs based optoelectronic devices.

Red-emitting polyaniline-based nanoparticle probe for pH-sensitive fluorescence imaging

Fluorescent probes based on semiconducting polymer nanoparticles (NPs) such as polyaniline (PANI) usually require external fluorophore doping to provide fluorescence function. Direct use of PANI-based NPs for bioimaging applications has been limited by PANI's weak blue fluorescence and aggregation-induced quenching in physiological medium. In this report, we developed a facile solid-state synthesis method to produce fluorescent polyaniline nanoparticles (FPNs) that are not only water-soluble but also exhibit high intensity and pH-sensitive red fluorescence. The FPNs showed high photoluminescence quantum yield (PLQY) of 19.3 % at physiological pH, which makes FPNs ideal for application as fluorescent nanoprobes in bioimaging. Moreover, we performed an in-depth study of photoluminescence dependence on pH and the phenomena of exciton-polaron quenching at low pH was highlighted. We also found that the ratio of emission intensity at 600 nm and 650 nm increased from 0.04 to 1.65 as pH was raised from 2.6 to 11.8, which could find its application in ratiometric pH sensing. FPNs exhibited excellent biocompatibility with >85 % cell viability for fibroblasts NIH/3 T3 and prostate cancer 22RV1 cells even at concentrations as high as 1000 μg/mL. In addition, fluorescence microscopy demonstrated concentration-dependent red fluorescence in the cytoplasm owing to the cellular uptake of FPNs in prostate cancer cells.

Responsive Carbonized Polymer Dots for Optical Super-resolution and Fluorescence Lifetime Imaging of Nucleic Acids in Living Cells

The rapid development of advanced optical imaging methods including stimulated emission depletion (STED) and fluorescence lifetime imaging microscopy (FLIM) has provided powerful tools for real-time observation of submicrometer biotargets to achieve unprecedented spatial and temporal resolutions. However, the practical imaging qualities are often limited by the performance of fluorescent probes, leading to unsatisfactory results. In particular, long-term imaging of nucleic acids in living cells with STED and FLIM remained desirable yet challenging due to the lack of competent probes combining targeting specificity, biocompatibility, low power requirement, and photostability. In this work, we rationally designed and synthesized a nanosized carbonized polymer dot (CPD) material, CPDs-3, with highly efficient and photostable emission for the super-resolution and fluorescence lifetime imaging of nucleic acids in living cells. The as-fabricated nanoprobe showed responsive emission properties upon binding with nucleic acids, providing an excellent signal-to-noise ratio in both spatial and temporal dimensions. Moreover, the characteristic saturation intensity value of CPDs-3 was as low as 0.68 mW (0.23 MW/cm²), allowing the direct observation of chromatin structures with subdiffraction resolution (90 nm) at very low excitation (<1 μW) and depletion power (<5 mW). Owing to its low toxicity, high photonic efficiency, and outstanding photostability, CPDs-3 was capable of performing long-term imaging both with STED and FLIM setups, demonstrating great potential for the dynamic study of nucleic acid functionalities in the long run.

Rapid detection of influenza A (H1N1) virus by conductive polymer-based nanoparticle via optical response to virus-specific binding

A recurrent pandemic with unpredictable viral nature has implied the need for a rapid diagnostic technology to facilitate timely and appropriate countermeasures against viral infections. In this study, conductive polymer-based nanoparticles have been developed as a tool for rapid diagnosis of influenza A (H1N1) virus. The distinctive property of a conductive polymer that transduces stimulus to respond, enabled immediate optical signal processing for the specific recognition of H1N1 virus. Conductive poly(aniline-co-pyrrole)-encapsulated polymeric vesicles, functionalized with peptides, were fabricated for the specific recognition of H1N1 virus. The low solubility of conductive polymers was successfully improved by employing vesicles consisting of amphiphilic copolymers, facilitating the viral titer-dependent production of the optical response. The optical response of the detection system to the binding event with H1N1, a mechanical stimulation, was extensively analyzed and provided concordant information on viral titers of H1N1 virus in 15 min. The specificity toward the H1N1 virus was experimentally demonstrated via a negative optical response against the control group, H3N2. Therefore, the designed system that transduces the optical response to the target-specific binding can be a rapid tool for the diagnosis of H1N1.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (Table S1 and Figs. S1-S8) is available in the online version of this article at 10.1007/s12274-021-3772-6.

Rapid conversion from common precursors to carbon dots in large scale: Spectral controls, optical sensing, cellular imaging and LEDs application

The commercial production of carbon dots will be concerned with the simplicity and energy consumption. Herein, maleic acid and m-phenylenediamine form elegantly simple sources for carbon dots. The two precursors are dissolved in formamid (abbreviated as FA) or N,N-dimethylformamide (abbreviated as DMF) and the dehydration-condensation processes have been performed at 30 min or 120 min under room temperature. No external energy/irradiations, reactants or high temperature will be required and the afforded carbon dots (abbreviated as CDs) are collected by extraction, centrifugation, dialysis and column chromatography. It has been found for the first time the choice of organic solvents has been correlated with emission color. The blue-emitting CDs (abbreviated as B-CDs) and green-emitting CDs (abbreviated as G-CDs) are yielded in FA and DMF respectively. Facts support that the increase of -CONH- units causes red-shift in emissions. The optical sensing of tetracycline has been explored and the detection limit of blue-emitting CDs is as low as 25 nM. Live cells exposed to B-CDs and G-CDs (0.5 mg/ml) show no apparent changes via both Cell Counting Kit-8 and Annexin V/7-AAD analysis. The blue and green fluorescent signals can be easily tracked in cells. It has been demonstrated that the two carbon dots can be fabricated as multiple-color light-emitting diodes (abbreviated as LEDs).

A ratiometric fluorescent probe for pH detection based on Ag2S quantum dots-carbon dots nanohybrids

In this study, a novel ratiometric fluorescent nanoprobe for pH monitoring has been developed by synthesizing red fluorescent Ag₂S quantum dots (Ag₂S QDs) and green fluorescent carbon dots (CDs) nanohybrids (Ag₂S CDs) in one pot using CDs as templates. The nanoprobe exhibits dual-emission peaks at 500 and 670 nm under a single-excitation wavelength of 450 nm. The red fluorescence can be selectively quenched by increasing pH, while the green fluorescence is an internal reference. Therefore, the change of the relative fluorescence intensity (I₅₀₀/I₆₇₀) in the ratiometric Ag₂S CDs probes can be used for pH sensing. The results revealed that I₅₀₀/I₆₇₀ of Ag₂S CDs probes was linearly related to pH variation between pH 5.4 and 6.8. Meanwhile, the Ag₂S CDs probes possessed a good reversibility along with pH changing between 5.0 and 7.0 without any interruption from common metal ions, proteins and other interferences.

Carbon dots for lysosome targeting and imaging of lysosomal pH and Cys/Hcy in living cells

The abnormal concentrations of both biothiols and pH in lysosomes are seriously related to many major diseases, such as Parkinson's and Alzheimer's diseases. Up to now, there are few reports that clearly illustrate the relationship between lysosomal pH and biothiols via fluorescence assay. Herein, novel carbon dots (Scy-CDs) are prepared with good water dispersibility and excellent photostability, and a large Stokes shift of 106 nm is exhibited under an excitation wavelength of 450 nm. The remarkable pH-dependent behavior of Scy-CDs is presented with the fluorescence quenching based on the donor-excited photoinduced electron transfer (d-PET) process. The pKa value is 5.30, which is in good agreement with the range of the normal and abnormal lysosomal pH. Upon the addition of cysteine (Cys) or homocysteine (Hcy), the d-PET process is effectively inhibited with fluorescence recovery totally. The significant co-localization of Scy-CDs with Lyso-Tracker Deep Red in HEp-2 cells and the Pearson correlation coefficient 0.88 strongly suggest that the Scy-CDs can target lysosomal pH and Cys/Hcy in living cells.

Development of the PANI/MWCNT Nanocomposite-Based Fluorescent Sensor for Selective Detection of Aqueous Ammonia

The present work reported the polyaniline (PANI) and multiwalled carbon nanotube (MWCNT)-based nanocomposite as a sensing material for the determination of aqueous ammonia by the enhanced fluorescence method. The excitation wavelength-dependent photoluminescence (PL) intensity has shown dual emission peaks at 340 and 380 nm that correspond to two different excitation energy states. The pH-based PL intensity and zeta potential variation were analyzed to optimize the suitable medium for aqueous ammonia sensing. Zeta potential was found to shift from 4 to -21 mV upon changing the pH of the the solution from acidic to alkaline medium. The fluorescence intensity of PANI/MWCNTs was found to increase upon increasing the pH from 3.0 to 6.0 (acidic region) and exhibits a plateau upon further increasing the pH from 7.0 to 12 (basic region). The PANI/MWCNT composite has shown a linear response to aqueous ammonia concentration varying from 25 to 200 μM with a correlation coefficient (R ²) of 0.99 and a limit of detection of 15.19 μM. The presence of relevant interference molecules and physiological ions had no influence on the detection of aqueous ammonia. Field-level study demonstrated that the level of aqueous ammonia can be determined selectively by using the PANI/MWCNT composite for various applications. The mechanism for the selective detection of aqueous ammonia is deliberated in detail.

Construction of a single quantum dot nanosensor with the capability of sensing methylcytosine sites for sensitive quantification of methyltransferase

CpG island methylation plays an important role in diverse biological processes including the regulation of imprinted genes, X chromosome inactivation, and tumor suppressor gene silencing in human cancer. Due to the dependence of DNA methylation on DNA methyltransferase (MTase) activity, DNA MTases have become the potential targets in anticancer therapy. Herein we demonstrate for the first time the construction of a single quantum dot (QD) nanosensor with the capability of sensing methylcytosine sites for sensitive quantification of M.SssI CpG methyltransferase (M.SssI MTase). We design a biotin-/phosphate-modified double-stranded DNA (dsDNA) substrate with a 5'-G-C-G-mC-3'/3'-mC-G-mC-G-5' site for sensing M.SssI MTase. In the presence of M.SssI MTase, the methylation-responsive sequence of the dsDNA substrate is methylated and cleaved by GlaI endonuclease, producing two dsDNA fragments with a free 3'-OH terminus. In the presence of terminal deoxynucleotidyl transferase (TdT), multiple Cy5-dATPs can be sequentially added to the free 3'-OH terminus of dsDNA fragments to obtain biotin-/multiple Cy5-labeled dsDNAs. The resultant biotin-/multiple Cy5-labeled dsDNAs can assemble on the surface of the streptavidin-coated QD to obtain a QD-dsDNA-Cy5 nanostructure in which the fluorescence resonance energy transfer (FRET) from the QD to Cy5 can occur. The emission of Cy5 can be simply quantified by single-molecule detection. By the integration of sensing methylcytosine sites and enzymatic polymerization, the sensitivity of this nanosensor has been significantly enhanced. This nanosensor can detect as low as 2.1 × 10-7 U μL-1 M.SssI MTase with good selectivity against other cytosine MTases, and it can be further applied for the screening of MTase inhibitors and complex biological sample analysis, holding great potential in clinical diagnosis and drug discovery.

Rational synthesis of highly efficient ultra-narrow red-emitting carbon quantum dots for NIR-II two-photon bioimaging

Despite the growing research interest in highly bio-compatible carbon quantum dots (CQDs) for bioimaging, the synthesis of red-emitting CQDs with high photoluminescence efficiency and a sharp emission spectrum remains a formidable challenge in this field. Herein, we established a rational strategy for the synthesis of highly efficient ultra-narrow red-emitting CQDs by adopting a conjugated aromatic amine precursor (tris(4-aminophenyl)amine, TAPA) and introducing oxidative radical reagents. The resultant CQDs, T-CQDs featured red PL (615 ± 2 nm) with a high photoluminescence quantum yield (84 ± 5%) and a narrow emission linewidth (FWHM = 27 ± 1 nm), which together represented one of the highest levels in the field of CQDs so far. The T-CQDs were then further analyzed from the spectral and structural aspects, and the repeatability and universality of this strategy have also been discussed. Finally, the T-CQDs were successfully applied for both one-photon imaging and two-photon imaging with various bio-samples, both in vitro and in vivo.

Lifetime-tunable room-temperature phosphorescence of polyaniline carbon dots in adjustable polymer matrices

Despite the excellent room-temperature phosphorescence (RTP) property of carbon dot (CD)-based RTP composites, the development of these emerging materials with finely tunable afterglow lifetimes still remains a challenge. Herein, for the first time, we report a series of pure organic RTP composite materials based on adjustable polyaniline carbon dots (PACDs) and polymer matrices (polyacrylic acid, polyacrylamide, and polyvinyl alcohol) with tunable RTP lifetimes. By using different polymer matrices and adjusting the functional groups of PACDs, the strength of hydrogen bonding between each polymer matrix and PACDs was regulated, and green RTP emissions with a tunable average lifetime ranging from 184 ms to 652 ms were also realized. In addition, taking advantage of their different persistent afterglow lifetimes, naked-eye-observable and time-resolved anti-counterfeit and data encryption patterns were prepared using these PACDs/polymer composites, demonstrating the potential application of these materials.

Benzoxazine monomer derived carbon dots as a broad-spectrum agent to block viral infectivity

Multiple viruses can cause infection and death of millions annually. Of these, flaviviruses are found to be highly prevalent in recent years with no distinctive antiviral therapies. Therefore, there is a desperate need for broad-spectrum antiviral drugs that can be active against a large number of existing and emerging viruses. Herein, we prepared a kind of benzoxazine monomer derived carbon dots (BZM-CDs) and demonstrated their infection-blocking ability against life-threatening flaviviruses (Japanese encephalitis, Zika, and dengue viruses) and non-enveloped viruses (porcine parvovirus and adenovirus-associated virus). It was found that BZM-CDs could directly bind to the surface of the virion, and eventually the first step of virus-cell interaction was impeded. The developed nanoparticles are active against both flaviviruses and non-enveloped viruses in vitro. Thus, the application of BZM-CDs may constitute an intriguing broad-spectrum approach to rein in viral infections.