Research on the Soft-Sensing Method of Indicator Diagram of Beam Pumping Unit.

An accurate calculation of the indicator diagram of a pumping unit is the key factor in analyzing the performance of an oilfield production and operation and in preparing and optimizing an oilfield development plan. Aiming at the problems of the poor stability of the conventional load-displacement sensor method and the wave equation method, owing to the influence of an alternating load on the force sensor and the difficulty in measuring the crank angle using the electrical parameter method, a new soft sensing method employing the input electrical parameters of the motor and the beam inclination has been proposed to obtain the indicator diagram. At first, this method is established based on the beam angle of the pumping unit, which is easily measured using the suspension point displacement mathematics calculation model and the torque factor. Subsequently, the electric motor input parameters, the parameters of the four-bar linkage, and the relationship between the polished rod load have been established. Finally, the motor and the beam angle of the measured electrical parameters have been substituted into the calculation of the suspension point displacement and load value and pull in accordance with the guidelines to eliminate the singularity mutation values. After processing the measured data through a Butterworth filter, the indicator diagram is obtained. The results of the engineering experiment and application show that the average relative error of the method is less than 3.95%, and the maximum relative error remains within 2% for 6 months, which verifies the stability of the soft sensing method.

Near Infrared-II Photothermal and Colorimetric Synergistic Sensing for Intelligent Onsite Dietary Myrosinase Profiling.

Myrosinase (Myr) is a type of critical ß-thioglucosidase enzyme activator essential for sustaining many functional foods to perform their health-promoting functions. An accurate and reliable Myr test is meaningful for food quality and dietary nutrition assessments, whereas the currently reported methods do not guarantee specificity and have high reliance on instrumentation, which are not suitable for rapid and onsite Myr screening especially in complex systems from various sources. Herein, we present a unique NIR-II absorption-based photothermal-responsive colorimetric biosensor for anti-interference onsite Myr determination and realization of rapid visualized outputs with the aid of smartphone calculation. Typically, assisted by glucose oxidase (GOx), Myr specifically converts the sinigrin substrate into hydrogen peroxide (H2O2) that can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by AuNPs to form a charge transfer complex (CTC) with NIR-II absorption and photothermal characters. Delightfully, such a proposed method is able to determine Myr within a wide range of 0 to 172.5 mU/mL with a detection limit down to 2.96 mU/mL. Moreover, simple, rapid, and real-time visual Myr identification in actual food-sourced samples could also be readily achieved by smartphone readout processing, with the promising advantages of anti-interference, high accuracy, and low cost as well as labor-saving and intelligence engagement, thus providing great feasibility for precise measurement in complex and dynamic dietary sample analysis. Overall, our proposed method presents a novel technology for onsite dietary Myr enzyme profiling, which is promising to be applied in the food industry for nutritional composition profiles, freshness evaluation, and quality assessment.

Enhancing the Reliability of SERS Detection in Ampicillin Using Oriented Tetrahedral Framework Nucleic Acid Probes and a Long-Range SERS Substrate.

Indirect surface-enhanced Raman scattering (SERS)-based methods are highly efficient in detecting and quantitatively analyzing trace antibiotics in complex samples. However, the poor reproducibility of indirect SERS assays caused by the diffusion and orientation changes of the probing molecules on SERS substrates still presents a significant challenge. To address this issue, this study reports the construction of a novel SERS sensing platform using tetrahedral framework nucleic acid (tFNA) as SERS probes in conjunction with a long-range SERS (LR-SERS) substrate. The tFNA was modified with sulfhydryl groups at three vertices and appended with a probing DNA at the remaining vertex, anchored on the substrate surface with a well-ordered orientation and stable coverage density, resulting in highly reproducible SERS signals. Owing to the weak SERS signal of tFNA inherited from its size being larger than the effective range of the enhancing electric field (E-field) of conventional SERS substrates, we utilized an LR-SERS substrate to enhance the signal of tFNA probes by capitalizing on its extended E-field. Correspondingly, the LR-SERS substrate demonstrated a 54-fold increase in the intensity of tFNA probes compared to the conventional substrate. Using this novel platform, we achieved a highly reliable detection of the antibiotic ampicillin with a wide linear range (10 fM to 1 nM), low detection limit (3.1 fM), small relative standard deviation (3.12%), and yielded quantitative recoveries of 97-102% for ampicillin in water, milk, and human serum samples. These findings, therefore, effectively demonstrate the achievement of highly reliable SERS detection of antibiotics using framework nucleic acids and an LR-SERS substrate.

Sensitive detection of extracellular hydrogen peroxide using plasmon-enhanced electrochemical activity on Pd-tipped Au nanobipyramids.

The fabrication of electroactive nanostructures with high electron concentration and specific electron transport is crucial for electrochemical sensing. In this study, a plasmon-enhanced electrochemical sensor has been developed for the detection of extracellular hydrogen peroxide (H2O2) from cancer cells, utilizing Pd-tipped Au nanobipyramids (PTA NBPs) as the electrocatalysts. Plasmonic PTA NBPs were synthesized by depositing Pd nanoparticles onto the tips of Au nanobipyramids (Au NBPs). Under excitation of localized surface plasmon resonance (LSPR), the PTA NBPs generate high-energy electron-hole pairs (e-/h+) on their surface. The generated electrons (e-) significantly enhance the electrochemical reduction of H2O2. Based on this, a plasmon-enhanced H2O2 electrochemical sensor is constructed with high sensitivity (986.57 µA mM-1 cm-2), low detection limit (0.02 µM), wide linear range (0.1 µM to 980 µM), and good stability and repeatability. Moreover, this sensor also enables the measurement of extracellular H2O2 derived from cancer cells (MCF-7), highlighting its potential applications in cellular biology and biomedical research.

Zwitterionic nanocapsules with pH- and thermal- responsiveness for drug-controlled release.

The construction of an environmentally responsive drug-release system is of great significance for the treatment of special diseases. In particular, the construction of nanomaterials with pH- and thermal-responsiveness, which can effectively encapsulate drugs and control drug release, is becoming hot research. In this study, zwitterionic nanocapsules with stable core-shell structures were synthesized by inverse reversible addition-fragmentation transfer miniemulsion interfacial polymerization. To further study the structure and performance of the nanocapsules, the prepared nanocapsules were characterized by transmission electron microscopy, dynamic light dispersion, and zeta potential analysis. It was found that the nanocapsules had dual pH- and thermal- responsiveness, and the average particle size ranged from 178 to 142 nm when the temperature changed from 25 °C to 40 °C. In addition, bovine serum albumin (BSA) was encapsulated into nanocapsules, and sustained release experiments were conducted at 10 °C and 40 °C. The results showed that nanocapsules as carriers of BSA could achieve the purpose of sustained release of drugs, and showed different sustained release curves at different temperatures. Finally,in vitrocytotoxicity tests were performed to demonstrate the feasibility of their biomedical application. It is believed that the dual pH- and thermal- responsive nanocapsules are promising for drug-controlled release.

Long-Range SERS Detection of the SARS-CoV-2 Antigen on a Well-Ordered Gold Hexagonal Nanoplate Film.

The development of an effective method for identifying severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) via direct viral protein detection is significant but challenging in combatting the COVID-19 epidemic. As a promising approach for direct detection, viral protein detection using surface-enhanced Raman scattering (SERS) is limited by the larger viral protein size compared to the effective electromagnetic field (E-field) range because only the analyte remaining within the E-field can achieve high detection sensitivity. In this study, we designed and fabricated a novel long-range SERS (LR-SERS) substrate with an Au nanoplate film/MgF2/Au mirror/glass configuration to boost the LR-SERS resulting from the extended E-field. On applying the LR-SERS to detect the SARS-CoV-2 spike protein (S protein), reagent-free detection achieved a low detection limit of 9.8 × 10-11 g mL-1 and clear discrimination from the SARS-CoV S protein. The developed technique also allows testing of the S protein in saliva with 98% sensitivity and 100% specificity.

Controlled Self-Assembly of a Close-Packed Gold Octahedra Array for SERS Sensing Exosomal MicroRNAs.

MicroRNAs (miRNAs) in exosomes can be transferred from parental cells to recipient cells by trafficking exosomes, and they are effective in regulating the gene expression of the recipient cells. Therefore, exosomal miRNAs play a vital role in cancer biology and could be potential biomarkers for cancer diagnosis and therapeutic responses. However, accurate detection of exosomal miRNAs is still challenging due to the low abundance of any given miRNA in exosomes. Herein, a surface-enhanced Raman scattering (SERS)-based sensor was developed for the quantitative determination of let-7a miRNAs in MCF-7 cell-derived exosomes (MCF-7 exosomes) using a close-packed and ordered Au octahedral array as a sensing platform. Au octahedra in the array uniformly stand on their triangular face. This kind of orientation produces "hot surfaces" rather than "hot spots" and greatly improves the detection sensitivity and uniformity. Let-7a detection with single-base specificity was thus achieved from the SERS intensity change induced by the structural switch of the probing DNA from a hairpin to a duplex in the presence of the target. The sensor showed a broad linear range (10 aM to 10 nM) and a low detection limit (5.3 aM) without using any signal amplification strategy. Moreover, this sensor could accurately detect target let-7a in MCF-7 exosomes and further value the impact of drug treatment on exosomal let-7a expression, indicating promising applications of the developed sensor for cancer diagnostics and therapy.

Dual-Aptamer-Assisted AND Logic Gate for Cyclic Enzymatic Signal Amplification Electrochemical Detection of Tumor-Derived Small Extracellular Vesicles.

Small extracellular vesicles (sEVs), often referred to as exosomes, are potential biomarkers for noninvasive cancer diagnosis. However, because of their phenotype heterogeneity, precise detection of tumor-derived sEVs is a great challenge. Herein, a dual-aptamer-assisted AND logic gate was fabricated for sensitive electrochemical detection of tumor-derived sEVs based on a cyclic enzymatic signal amplification strategy. Four different tumor-derived sEVs were used to verify the feasibility of the AND logic gate, and CCRF-CEM sEVs were successfully detected by this assay. The electrochemical assay shows a good linear response from 4 × 103 to 8 × 107 particles/µL, with a detection limit of 920 particles/µL, for CCRF-CEM sEVs, indicating potential application in accurate cancer diagnostics.

Plasmonic SERS Biosensor Based on Multibranched Gold Nanoparticles Embedded in Polydimethylsiloxane for Quantification of Hematin in Human Erythrocytes.

This work reports a plasmonic surface-enhanced Raman scattering (SERS) biosensor that allows for quantitative analysis of hematin in erythrocytes without the need of separating it from hemoglobin (Hb). The biosensor exploits the tunable localized surface plasmon resonance (LSPR) characteristics of multibranched gold nanoparticles (M-AuNPs) and the strong plasmon coupling between an Au thin film and a flexible substrate consisting of M-AuNPs embedded in polydimethylsiloxane (PDMS) (i.e., M-AuNP-embedded PDMS substrate). In the assay, the hematin (or hematin-containing erythrocyte hemolysate) was deposited on Au film surface and covered with M-AuNP-embedded PDMS. Strong SERS signals were generated under excitation at 785 nm; the signals were sensitive to hematin concentration but not to several common coexisting biological substances. The intensities of the SERS signal (at 1623 cm-1) displayed a wide linear range using hematin concentrations in a range of at least ∼1.5 nM-1.1 µM; the limit of detection (LOD) was ∼0.03 ± 0.01 nM at a signal/noise (S/N) of 3. This assay is simple and sensitive without tedious separation procedures, thereby saving time and enhancing efficiency. This biosensor can be used to determine hematin concentration in human erythrocyte cytosols giving concentrations of ∼18.5 ± 4.5 (by averaging eight samples) and 51.5 ± 6.2 µM (by averaging three samples) for healthy and sickle erythrocytes, respectively, making it a potential application in clinical detection.

Electrochemical Sensing of Exosomal MicroRNA Based on Hybridization Chain Reaction Signal Amplification with Reduced False-Positive Signals.

MicroRNAs (miRNAs) in cancer cell-derived exosomes are important cancer biomarkers. Herein, a sensitive hybridization chain reaction (HCR) electrochemical assay was fabricated for the detection of exosomal microRNA-122 (miR-122). The hairpin DNA (hpDNA) probes were first immobilized on the surface of a gold electrode. In the presence of miR-122, the hairpin structure of the hpDNA could be opened and triggered the HCR through the cross-opening and hybridization of two helper DNA hairpins. Long nicked double helixes generated from HCR are used to capture more RuHex and increase the signal of differential pulse voltammetry (DPV). In this assay, the density of the hpDNA probes on the surface of the gold electrode was precisely controlled by the simultaneous immobilization of hpDNA and short 12 nucleotides single-stranded DNA (S-12), providing a very high amplification efficiency. More importantly, the false positive signal could be reduced or completely eliminated by applying exonuclease I (Exo I) before the introduction of target miR-122. Under optimal conditions, the assay offers very high sensitivity with an attomolar level detection limit, a linear range with 9 orders of magnitude, and specificity in single mismatch discrimination. This sensitive electrochemical assay could successfully evaluate the miR-122 concentration in different cancer-derived exosomes, indicating its potential use in cancer diagnostics.

A facile and label-free electrochemical aptasensor for tumour-derived extracellular vesicle detection based on the target-induced proximity hybridization of split aptamers.

Facile detection of tumour-derived extracellular vesicles (EVs) is crucial to cancer diagnosis. Herein, a facile and label-free electrochemical aptasensor was fabricated to detect tumour-derived EVs based on the target-induced proximity hybridization of split aptamers. In this assay, two designed oligonucleotide probes containing fragments of a protein tyrosine kinase-7 (PTK7) aptamer were used to recognize and capture EVs containing PTK7. In the presence of target EVs, the aptamer-target ternary complex could induce proximity hybridization and form a DNA duplex on the electrode. The DNA duplex could bind more electroactive Ru(NH3)63+ through electrostatic attraction, resulting in an increased cathodic current signal. By virtue of the excellent electrochemical signal reporter RuHex, the specificity of the aptamer and proximity ligation, a facile EV electrochemical aptasensor with a detection limit of 6.607 × 105 particles per mL was realized. Furthermore, this aptasensor showed good selectivity to distinguish different tumour-derived EVs and was applied to detect EVs in complex biological samples. The proposed electrochemical aptasensor can be further extended to the detection of other EVs, thus showing great potential in clinical diagnosis.

Structure-controlled zwitterionic nanocapsules with thermal-responsiveness.

A facile approach is established to prepare zwitterionic nanocapsules (ZN C s) with controlled diameters and core/shell structures based on an inverse reversible addition-fragmentation transfer (RAFT) miniemulsion interfacial polymerization method. The diameters and core volume fractions of ZNCs can be tuned finely from 61 to 220 nm and from 0.22 to 0.61, respectively. Furthermore, the thermal-responsive property of the prepared zwitterionic nanocapsules was systematically studied relating to core/shell ratios and cross-linking degrees. These ZNCs could be particularly useful in constructing polymeric materials with well-defined nanoporous structures for nano-void membranes, drug delivery devices and catalytic carriers.

A Chemically Soldered Polyoxometalate Single-Molecule Transistor.

Polyoxometalates have been proposed in the literature as nanoelectronic components, where they could offer key advantages with their structural versatility and rich electrochemistry. Apart from a few studies on their ensemble behaviour (as monolayers or thin films), this potential remains largely unexplored. We synthesised a pyridyl-capped Anderson-Evans polyoxometalate and used it to fabricate single-molecule junctions, using the organic termini to chemically "solder" a single cluster to two nanoelectrodes. Operating the device in an electrochemical environment allowed us to probe charge transport through different oxidation states of the polyoxometalate, and we report here an efficient three-state transistor behaviour. Conductance data fits a quantum tunnelling mechanism with different charge-transport probabilities through different charge states. Our results show the promise of polyoxometalates in nanoelectronics and give an insight on their single-entity electrochemical behaviour.

Label-Free Raman Observation of TET1 Protein-Mediated Epigenetic Alterations in DNA.

Epigenetic modifications of DNA are known to modulate gene activity and expression and are believed to result in genetic diseases, such as cancer. Four modified cytosines were discovered in mammalian genomes: 5-methycytoine (5mC), 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxycytosine (5caC). They are regarded as DNA epigenetic markers and play key roles in the regulation of the dynamic balance between DNA methylation and demethylation. Although detection approaches toward 5mC are ubiquitous, few assays have reported the simultaneous determination of all four modified cytosines as well as monitoring of their dynamic alterations. Here, we developed a label-free surface enhanced Raman spectroscopy (SERS)-based method for directly sensing the four DNA modifications by using a plasmonic gold nanohole array (PGNA) with well-controlled hot spots and an open surface as the substrate. This method is based on identifying SERS spectral features resulting from DNA base modifications. Our study shows that 5mC, 5hmC, 5fC, and 5caC exhibit distinct Raman spectroscopic signatures at 785, 660, 1450, and 1680 cm-1, respectively. Moreover, the developed method can be used for tracking of the dynamic alterations among these four modified cytosines in DNA mediated by the ten-eleven translocation (TET) protein. The dynamic stepwise conversion from 5mC into 5hmC, 5fC, and 5caC is further demonstrated to be a typical three-step consecutive reaction with rate constants of 0.6, 0.25, and 0.15 min-1, respectively, which has not been achieved before via a SERS-based method.

Graphene Quantum Dots Wrapped Gold Nanoparticles with Integrated Enhancement Mechanisms as Sensitive and Homogeneous Substrates for Surface-Enhanced Raman Spectroscopy.

Rational engineering of highly stable and Raman-active nanostructured substrates is still urgently in demand for achieving sensitive and reliable surface-enhanced Raman spectroscopy (SERS) analysis in solution phase. Herein, monodisperse N-doping graphene quantum dots wrapped Au nanoparticles (Au-NGQD NPs) were facilely prepared, and further their applications as substrates in SERS-based detection and cellular imaging have been explored. The as-prepared Au-NGQD NPs exhibit superior long-term stability and biocompatibility, as well as large enhancement capability due to the integration of electromagnetic and chemical enhancements. The practical applicability of the Au-NGQD NPs was verified via the direct SERS tests of several kinds of aromatics in solution phase. Finite-difference time-domain simulations in combination with density functional theory calculation were also successfully used to explain the enhancement mechanism. Furthermore, the Au-NGQD NPs were conjugated with 4-nitrobenzenethiol (4-NBT, as reporter) and 4-mercaptophenylboronic acid (MPBA, as targeting element) to construct the MPBA/4-NBT@Au-NGQD probes, which could specifically recognize glycan-overexpressed cancer cells through SERS imaging on a cell surface. The prepared Au-NGQDs show great potential as superior SERS substrates in solution phase for on-site Raman detection.

An electrochemiluminescent aptasensor for amplified detection of exosomes from breast tumor cells (MCF-7 cells) based on G-quadruplex/hemin DNAzymes.

Exosomes are non-invasive biomarkers for cancer diagnosis. Herein, we describe an electrochemiluminescent (ECL) aptasensor for the detection of exosomes from breast tumor cells. Mercaptopropionic acid (MPA)-modified Eu3+-doped CdS nanocrystals (MPA-CdS:Eu NCs) and H2O2 were used as ECL emitters and coreactant, respectively. The exosomes are recognized and captured by the CD63 aptamer, and then form a G-quadruplex/hemin DNAzyme, which efficiently catalyzes the decomposition of H2O2, resulting in the decreased ECL signal of MPA-CdS:Eu NCs. The exosomes from breast tumor cells (MCF-7 cells) can be detected in the range of 3.4 × 105 to 1.7 × 108 particles per mL. The limit of detection (LOD) was estimated to be 7.41 × 104 particles per mL at a signal-to-noise ratio of 3. The aptasensor has been successfully used to detect exosomes in the serum.

Highly Sensitive Electrochemical Detection of Tumor Exosomes Based on Aptamer Recognition-Induced Multi-DNA Release and Cyclic Enzymatic Amplification.

Sensitive and specific detection of tumor exosomes is of great significance for early cancer diagnosis. In this paper, we report an aptamer strategy for exosome detection based on aptamer recognition-induced multi-DNA release and cyclic enzymatic amplification. First, we use aptamer-magnetic bead bioconjugates to capture tumor exosomes derived from LNCaP cells, leading to the release of three kinds of messenger DNAs (mDNAs). After magnetic separation, the released mDNAs hybridized with the probe DNAs immobilized on a gold electrode. Electroactive Ru(NH3)63+ was used as the signal reporter because of its electrostatic attraction to DNA. Subsequent Exo III cyclic digestion caused the electrochemical signal to "turn off". Because the electrochemical signal reflects the concentration of Ru(NH3)63+ and the concentration of Ru(NH3)63+ is correlated with the mDNA concentration, which is correlated with the exosome concentration, the tumor exosomes can be detected by examining the decrease in the peak current of Ru(NH3)63+. In this paper, the signal was amplified by the numerous mDNAs released from the magnetic bead and the Exo III-assisted mDNA recycling. Under the optimal conditions, a detection limit down to 70 particles/µL was achieved, which is lower than the LODs of most currently available methods. Furthermore, this assay can be used to detect tumor exosomes in complex biological samples, demonstrating potential application in real sample diagnosis.

Dual-signal ratiometric electrochemiluminescence assay for detecting the activity of human methyltransferase.

In this paper, a dual-signal ratiometric electrochemiluminescence (ECL) assay was developed to detect human DNA (cytosine-5)-methyltransferase1 (DNMT1) activity. Mercaptopropionic acid (MPA)-modified Eu3+-doped CdS nanocrystals (MPA-CdS:Eu NCs) and luminol were used as two different ECL emitters, which showed ECL signals at different electrochemical potentials. The resultant ECL peaks exhibited opposite trends in the DNMT1 system. According to the ratio of the ECL responses of CdS to luminol, the DNMT1 activity was detected in the range of 1.0-30.0 U mL-1 in buffer solution. The limit of detection (LOD) was estimated to be 0.07 U mL-1 at a signal-to-noise ratio of 3. The assay was extended to detect the DNMT1 activity from crude lysates of cancer cells, along with the effect of DNMT1 inhibitors such as 5-aza and 5-aza-2'-dC.

Electrochemical signal-amplified detection of 5-methylcytosine and 5-hydroxymethylcytosine in DNA using glucose modification coupled with restriction endonucleases.

The levels of 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) in DNA (5-mC-DNA and 5-hmC-DNA) are strongly correlated with cancer occurrence and development. The ability to distinguish and quantitatively detect them is important for cancer research. We have developed a hybridization chain reaction (HCR)-based electrochemical assay for the signal-amplified detection of the relative contents of 5-mC-DNA and 5-hmC-DNA. The DNA duplexes (containing 5-mC-DNA and 5-hmC-DNA with different percentages) were modified on a gold electrode. Electroactive [Ru(NH3)6]3+ (RuHex) was used as the signal reporter, because it binds to DNA double strands. The duplexes can be cleaved by MspJI endonuclease without HCR, and result in a small peak current. However, the cleavage can be blocked after the 5-hmC-DNA duplex is converted to ß-glucosyl-5-hydroxymethylcytosine (ß-glu-5-hmC) by T4 ß-glucosyltransferase (T4 ß-GT), and with the addition of helper DNA, a long double-helix DNA was formed through HCR. A significantly amplified peak current can be achieved due to the adsorption of numerous RuHex. The electrochemical signal of RuHex is correlated to the content of 5-hmC-DNA. Upon fixing the total quantity of 5-mC-DNA and 5-hmC-DNA on the electrode, the signals increase with the increase in the percentage of 5-hmC-DNA for the HCR. With this assay, a detection limit of 0.05% for 5-hmC-DNA was achieved.

Oxygen sensitive polymeric nanocapsules for optical dissolved oxygen sensors.

Immobilization of the oxygen-sensitive probes (OSPs) in the host matrix greatly impacts the performance and long-term usage of the optical dissolved oxygen (DO) sensors. In this work, fluorescent dyes, as the OSPs, were encapsulated with a crosslinked fluorinated polymer shell by interfacial confined reversible addition fragmentation chain transfer miniemulsion polymerization to fabricate oxygen sensitive polymeric nanocapsules (NCs). The location of fluorescent dyes and the fluorescent properties of the NCs were fully characterized by fourier transform infrared spectrometer, x-ray photoelectron spectrometer and fluorescent spectrum. Dye-encapsulated capacity can be precisely tuned from 0 to 1.3 wt% without self-quenching of the fluorescent dye. The crosslinked fluorinated polymer shell is not only extremely high gas permeability, but also prevents the fluorescent dyes from leakage in aqueous as well as in various organic solvents, such as ethanol, acetone and tetrahydrofuran (THF). An optical DO sensor based on the oxygen sensitive NCs was fabricated, showing high sensitivity, short response time, full reversibility, and long-term operational stability of online monitoring DO. The sensitivity of the optical DO sensor is 7.02 (the ratio of the response value in fully deoxygenated and saturated oxygenated water) in the range 0.96-14.16 mg l-1 and the response time is about 14.3 s. The sensor's work curve was fit well using the modified Stern-Volmer equation by two-site model, and its response values are hardly affected by pH ranging from 2 to 12 and keep constant during continuous measurement for 3 months. It is believed that the oxygen sensitive polymeric NCs-based optical DO sensor could be particularly useful in long-term online DO monitoring in both aqueous and organic solvent systems.