Rapid photothermal assay for ultrasensitive point-of-care detection of tumor markers based on a filter membrane.

An ultrasensitive photothermal assay was designed for point-of-care testing (POCT) of tumor markers based on a filter membrane. Firstly, Cu2-xSe was successfully encapsulated in liposome spheres with biotin on the surface and connected to carcinoembryonic antigen (CEA) aptamer with 3'end modified biotin by streptavidin. Secondly, the CEA antibody was successfully modified on the surface of the nitrocellulose membrane through simple incubation. Finally, the assay process was completed using a disposable syringe, and the temperature was recorded using a handheld infrared temperature detector. In the range 0-50 ng mL-1, the temperature change of the nitrocellulose membrane has a strong linear relationship with CEA concentration, and the detection limit is 0.097 ng mL-1. It is worth noting that the entire testing process can be easily performed in 10 min, much shorter than traditional clinical methods. In addition, this method was successfully applied to the quantitative determination of CEA levels in human serum samples with a recovery of 96.2-103.3%. This rapid assay can be performed by "one suction and one push" through a disposable syringe, which is simple to operate, and the excellent sensitivity reveals the great potential of the proposed strategy in the POCT of tumor biomarkers.

An intelligent Cu/ZIF-8-based nanodrug delivery system for tumor-specific and synergistic therapy via tumor microenvironment-responsive cascade reaction.

An intelligent nanodrug delivery system (Cu/ZIF-8@GOx-DOX@HA, hereafter CZGDH) consisting of Cu-doped zeolite imidazolate framework-8 (Cu/ZIF-8, hereafter CZ), glucose oxidase (GOx), doxorubicin (DOX), and hyaluronic acid (HA) was established for targeted drug delivery and synergistic therapy of tumors. The CZGDH specifically entered tumor cells through the targeting effect of HA and exhibited acidity-triggered biodegradation for subsequent release of GOx, DOX, and Cu2+ in the tumor microenvironment (TME). The GOx oxidized the glucose (Glu) in tumor cells to produce H2O2 and gluconic acid for starvation therapy (ST). The DOX entered the intratumoral cell nucleus for chemotherapy (CT). The released Cu2+ consumed the overexpressed glutathione (GSH) in tumor cells to produce Cu+. The generated Cu+ and H2O2 triggered the Fenton-like reaction to generate toxic hydroxyl radicals (·OH), which disrupted the redox balance of tumor cells and effectively killed tumor cells for chemodynamic therapy (CDT). Therefore, synergistic multimodal tumor treatment via TME-activated cascade reaction was achieved. The nanodrug delivery system has a high drug loading rate (48.3 wt%), and the three-mode synergistic therapy has a strong killing effect on tumor cells (67.45%).

Dual-mode photothermal/chemiluminescence vertical flow assay for sensitive point-of-care detection of carcinoembryonic antigen using Cu2-xAgxS@liposome on a filter membrane.

Conventional lateral flow assays based on colorimetry and fluorescence still have shortages in sensitivity and selectivity due to the severe background interference from complex human fluid sample matrices. In this work, Cu2-xAgxS nanocrystals with high photothermal conversion efficiency and good peroxidase-like activity were synthesized and applied in the construction of a dual-mode near-infrared-photothermal/chemiluminescence (CL) vertical flow assay of carcinoembryonic antigen (CEA). These two-mode principles showed nearly zero background and the synthesized Cu2-xAgxS exhibited a high photothermal conversion efficiency of 75.23%, enabling the luminol-H2O2 CL system to have over 4 min of chemiluminescence. By combining filter membrane enrichment, Cu2-xAgxS@liposome encapsulation amplification, and nanozyme catalysis, a dual-mode photothermal/CL portable assay was constructed for sensitive and accurate detection of CEA in serum, with linear ranges of 0.02-40 and 0.001-30 ng mL-1, and detection limits of 0.0023 and 0.00029 ng mL-1, respectively. Furthermore, a smartphone application and a 3D printing device were combined for point-of-care testing. This assay can be completed within 20 min, with simple operation and no need for large instruments. It exhibited good sensitivity, selectivity, and stability, and is expected to be used in early diagnosis and prevention of relevant diseases in resource-limited areas.

A high-resolution time-frequency analysis technique based on bi-directional squeezing and its application in fault diagnosis of rotating machinery.

Most of the signals in the field of industrial engineering are nonstationary signals, and the accurate description of the time-frequency (TF) characteristics of nonstationary signals is important for the advancement of industrial engineering. Instantaneous frequency (IF) and group delay (GD) are common TF features used to describe nonstationary signals. Time-reassigned synchrosqueezing transform and synchrosqueezing transform are two TF analysis tools that can accurately characterize the GD and IF of nonstationary signals by squeezing the TF coefficients in the time direction and frequency direction, respectively. However, it is difficult for such two techniques to accurately characterize IF and GD simultaneously. A novel method called time-frequency squeezing transform is introduced in this paper to conquer this drawback. The technique first uses the short-time Fourier transform to calculate the time-frequency representation (TFR) of a signal, and then divides the TFR into two parts according to a chirp rate estimator. The subdivided TFR parts are then squeezed in the frequency and time directions to accurately characterize the IF and GD, respectively, and the two squeezed results are added to form a high-resolution result. The effectiveness of the proposed technique is demonstrated with numerical and experimental signals.

An intelligent readable and capture-antibody-independent lateral flow immunoassay based on Cu2-xSe nanocrystals for point-of-care detection of Escherichia coli O157:H7.

Escherichia coli (E. coli) O157:H7 is a common foodborne pathogen which can cause serious harm. It is particularly important to establish a simple and portable method to achieve on-site pathogen detection. In this study, a capture-antibody-independent lateral flow immunoassay (LFIA) was constructed based on Cu2-xSe nanocrystals (Cu2-xSe NCs) for rapid detection of E. coli O157:H7. Cu2-xSe NCs can not only be regarded as the "nano-antibody" for the recognition of E. coli O157:H7 through electrostatic adsorption, but also as nanozymes that show good peroxidase-like catalytic activity. The formed compound of E. coli O157:H7 and Cu2-xSe NCs would be captured by a detection antibody on the T line due to the specific recognition of the antibody and E. coli O157:H7. Then, Cu2-xSe NCs could catalyze the oxidation of TMB by H2O2 to generate oxTMB, thereby generating blue bands. Meanwhile, we developed a mobile app for rapid data analysis. Under the optimal reaction conditions, E. coli O157:H7 could be detected within 70 min. The detection limit of this method was 2.65 × 105 CFU mL-1 with good specificity and stability. Additionally, it could achieve on-site rapid detection of E. coli O157:H7 in environmental water samples, providing a promising biosensor for portable pathogen detection.

pH-Triggered visual detection of Escherichia coli based on the co-assembly of bacitracin and thymolphthalein.

A novel probe for bacteria was simply synthesized through the solvent-induced co-assembly of bacitracin (AMP) and thymolphthalein (TP) without complicated modification. Combining with aptamer-Fe3O4, AMP/TP nanoparticles were used for the colorimetric detection of Escherichia coli with good sensitivity through the NaOH-triggered blue color and a smartphone-based App.

A methylene blue-functionalized DNA concatemer for the construction of a turn-off fluorescent immunosensor for the sensitive detection of carcinoembryonic antigen.

This study showed a method of synthetization of a methylene blue-functionalized DNA concatemer via hybridization chain reaction (HCR) used for turn-off fluorescence detection of carcinoembryonic antigen (CEA). During the experiments, CEA aptamers and the methylene blue-functionalized DNA concatemer were modified onto the surface of Au nanoparticles (AuNPs). By detecting the signal of remaining methylene blue in the solution that has not been embedded in the DNA concatemer, we obtained an amplified decrease of the fluorescence signal at 695 nm for CEA. The linear range was from 0.1 to 80 ng mL-1 with a limit of detection at 75 pg mL-1 for CEA determination. Our results showed that the proposed method had good selectivity and could generate satisfactory results for clinical serum sample determination. Based on the positive outcomes obtained, we determined that the method provided a sensitive and accurate way for early clinical diagnosis of cancer disease.

Iodide-Mediated Etching of Gold Nanostar for the Multicolor Visual Detection of Hydrogen Peroxide.

A multicolor visual method for the detection of hydrogen peroxide (H2O2) was reported based on the iodide-mediated surface etching of gold nanostar (AuNS). First, AuNS was prepared by a seed-mediated method in a HEPES buffer. AuNS shows two different LSPR absorbance bands at 736 nm and 550 nm, respectively. Multicolor was generated by iodide-mediated surface etching of AuNS in the presence of H2O2. Under the optimized conditions, the absorption peak Δλ had a good linear relationship with the concentration of H2O2 with a linear range from 0.67~66.67 µmol L-1, and the detection limit is 0.44 µmol L-1. It can be used to detect residual H2O2 in tap water samples. This method offered a promising visual method for point-of-care testing of H2O2-related biomarkers.

Gas-Mediated Immunoassay for the Carcinoembryonic Antigen at Atmospheric Pressure with Smartphone Coupling with the Fluorescence Quenching Length of Perovskite Capillary.

By combining the photothermal properties of the 3,3',5,5'-tetramethylbenzidine oxidation product (TMBox) with the sensitive quenching of perovskite fluorescence by ammonia gas, a gas-mediated immunoassay at atmospheric pressure was constructed, which took the fluorescence quenching length of perovskite fluorescent capillary as the signal output. First, a CsPbBr3 perovskite with surface modification of 3-aminopropyl triethoxysilane was synthesized by thermal injection and decorated to the capillary wall by glutaraldehyde cross-linking. In the presence of H2O2 and the tumor marker carcinoembryonic antigen (CEA), TMB was oxidized to TMBox by the horseradish peroxidase (HRP)-labeled CEA antibody. The photothermal effect of TMBox at 808 nm laser irradiation increases the concentration of ammonia gas, and the prepared fluorescent capillary can respond sensitively to ammonia gas. The fluorescence quenching length can be observed by the naked eye for a semiquantitative evaluation of CEA concentration. At the same time, we developed a mobile APP for the first time to measure the fluorescence quenching length. In the range of 0-20 ng mL-1, the quenching length increased linearly with the increase in CEA concentration, and the detection limit was 0.078 ng mL-1. This method has been successfully used for the detection of CEA in human serum with a recovery of 95.8%-106.5%.

Fluorescence immunosensor based on functional nanomaterials and its application in tumor biomarker detection.

An immunosensor is defined as an analytical device that detects the binding of an antigen to its specific antibody by coupling an immunochemical reaction to the surface of a device called a transducer. Fluorescence immunosensing is one of the most promising immunoassays at present, and has the advantages of simple operation, fast response and high stability. A traditional fluorescence immunosensor often uses an enzyme-labelled antibody as a recognition unit and an organic dye as a fluorescence probe, so it is easily affected by environmental factors with low sensitivity. Nanomaterials have unique photostability, catalytic properties and biocompatibility, which open up a new path for the construction of stable and sensitive fluorescence immunosensors. This paper briefly introduces different kinds of immunosensors and the role of nanomaterials in the construction of immunosensors. The significance of fluorescent immunosensors constructed from functional nanomaterials to detect tumor biomarkers was analyzed, and the strategies to further improve the performance of fluorescent immunosensors and their future development trend were summarized.

Polydopamine-Functionalized Copper Peroxide/ZIF-8 Nanoparticle-Based Fluorescence-Linked Immunosorbent Assay for the Sensitive Determination of Carcinoembryonic Antigen by Self-Supplied H2O2 Generation.

Copper peroxide/zeolitic imidazolate framework/polydopamine nanoparticles (CP/ZIF-8/PDA)-based fluorescence-linked immunosorbent assay (FLISA) was designed for the sensitive and high-throughput determination of carcinoembryonic antigen (CEA) by self-supplied H2O2 generation. Specifically, the CEA aptamer was modified on the surface of CP/ZIF-8/PDA to form an immunoprobe. The structures of CP and ZIF-8 could be broken under acidic conditions, and produced the Cu2+ and H2O2 due to the dissociation the CP. A subsequent Fenton-type reaction of Cu2+ and H2O2 generated hydroxyl radical (·OH). o-phenylenediamine (OPD) was oxidized by the ·OH to form 2, 3-diaminophenazine (DPA) with a significant fluorescence signal. CP/ZIF-8/PDA could be used as an efficient Fenton-type reactant to generate a large amount of ·OH to promote OPD oxidation. The sensitive detection of CEA could be realized. Under optimal conditions, the FLISA platform displayed a linear detection range from 0.01 to 20 ng mL-1 with a detection limit of 7.6 pg mL-1 for CEA. This strategy has great application potential for sensitive and high-throughput determination for other biomarkers in the field of biomedicine.

Homogeneous photoelectrochemical biosensor for sensitive detection of omethoate via ALP-mediated pesticide assay and Bi2S3@Bi2Sn2O7 heterojunction as photoactive material.

A simple homogeneous photoelectrochemical (PEC) sensing platform based on an alkaline phosphatase (ALP)-mediated pesticide assay was established for the sensitive detection of omethoate (OM). The Bi2S3@Bi2Sn2O7 heterojunction was used as a photoactive material to provide stable background photocurrent signals. The inhibition of OM on ALP and PEC determination was carried out in the homogeneous system. In the absence of OM, dephosphorylation of L-ascorbic acid 2-phosphate trisodium salt (AAP) was catalyzed by ALP to produce the enzyme-catalyzed product (L-ascorbic acid, AA). AA, as an electron donor, could capture photogenerated holes on the Bi2S3@Bi2Sn2O7 heterojunction, thus inhibiting the recombination of electron holes to achieve an increase of the photocurrent signal. When the OM was introduced, the enzyme activity of ALP was reduced due to the organophosphorus pesticides (OPs)-based enzyme inhibition, and the AA produced by catalytic hydrolysis was also reduced, thus reducing the photocurrent signal. Compared with the traditional PEC sensor for OPs, this homogeneous PEC sensor avoided immobilization procedures, covalent labeling, separation, and the steric hindrance effect caused by immobilized biomolecules, which achieved high recognition efficiency and caused a reduction in analysis time. Additionally, an ALP-mediated pesticide assay for the determination of OPs with a simplified experimental process further improved the stability and reproducibility of the PEC sensor. The PEC sensor showed high sensitivity to the target OM within a dynamic range of 0.05 ~ 500 ng mL-1, and the detection limit was 0.0146 ng mL-1. Additionally, the PEC biosensing system showed good selectivity and anti-interference ability, and exhibited a satisfactory result in spinach and mustard samples. A homogeneous PEC biosensor based on ALP inhibition strategy was constructed for OM detection in vegetable samples via Bi2S3@Bi2Sn2O7 heterojunction as the photoactive substrate material.

Bacitracin-Functionalized Dextran-MoSe2 with Peroxidase-like and Near-Infrared Photothermal Activities for Low-Temperature and Synergetic Antibacterial Applications.

Bacitracin (an antimicrobial peptide, AMP)-modified dextran-MoSe2 nanosheets (AMP/dex-MoSe2 NSs) were constructed and applied for low-temperature and synergetic antibacterial applications. The near-infrared (NIR) photothermal and peroxidase-like activities of dex-MoSe2 were combined with the bacterial membrane-binding ability of AMP through electrostatic adsorption, and a multimode antibacterial method was realized. H2O2 was converted into a hydroxyl radical (·OH) by AMP/dex-MoSe2, which exhibits a higher antibacterial activity and can avoid the toxicity of a high concentration of H2O2. Importantly, the production of ·OH and the antibacterial efficiency of AMP/dex-MoSe2 were accelerated by low-temperature heat sterilization with NIR irradiation. Owing to the AMP-guided binding and destruction effect to the bacterial membrane, AMP/dex-MoSe2 shows a better antibacterial effect on Gram-negative Escherichia coli under NIR irradiation as compared to catalytic treatment or NIR photothermal sterilization alone. Furthermore, the cytotoxicity and hemolysis of AMP/dex-MoSe2 were weak and in a relatively safe range. This multimode antibacterial strategy based on the AMP/dex-MoSe2 nanozyme will pave a way for the development of more safe and efficient antibacterial applications.

A ratiometric electrochemical biosensor via alkaline phosphatase mediated dissolution of nano-MnO2 and Ru(III) redox recycling for the determination of dimethoate.

A sensitive and ratiometric electrochemical biosensor was developed for the determination of dimethoate via alkaline phosphatase (ALP) mediated dissolution of nano-MnO2 and [Ru(NH3)6]3+(Ru(III)) redox recycling. The electroactive probe Ru(III) was adsorbed on the nano-MnO2 with the high specific surface area through electrostatic interaction to form the MnO2-Ru(III) nanocomposite, which was then fixed on the surface of the glassy carbon electrode. When the dimethoate inhibited the catalytic activity of ALP in a homogeneous system, the hydrolysate L-ascorbic acid (AA) produced by ALP hydrolysis of L-ascorbic acid-trisodium 2-phosphate (AAP) decreased. The solution was then incubated with a glassy carbon electrode modified by MnO2-Ru(III). At this time, only a small amount of MnO2-Ru(III) was decomposed and Ru(III) was rapidly electroreduced to Ru(II) on the surface of the electrode. The in-situ produced Ru(II) was chemically oxidized back to Ru(III) by Fe(III). The redox recycling of Ru(III) was completed and the Ru(III) reduction current signal was amplified. The process consumed part of Fe(III) to reduce the reduction current signal of Fe(III), and the ratio of the two reduction currents (IRu(III)/IFe(III)) increased significantly. The IRu(III)/IFe(III) value increased with the increase of dimethoate concentration in the linear range of 0.01-300 ng mL-1, and the detection limit was 6.3 pg mL-1. It has been successfully applied to the determination of dimethoate in oilseed rape and lettuce with a satisfactory result.

Multicolor and photothermal dual-mode assay of alkaline phosphatase based on the UV light-assisted etching of gold nanorods.

A multicolor and photothermal dual-mode assay for sensitive alkaline phosphatase (ALP) determination was realized based on the 3,3',5,5'-tetramethylbenzidine (TMB)-induced etching of gold nanorods (AuNRs). TMB was oxidized under ultraviolet light irradiation to form TMB+. In the presence of ALP, ascorbic acid phosphate (AAP) is converted to ascorbic acid, which can then reduce the levels of TMB+, resulting in lower concentrations of TMB+. The remaining TMB+ was transformed into TMB2+ after the addition of HCl solution. AuNRs were etched by TMB2+ to produce a multicolor and photothermal change. Based on the degree of AuNRs etching, this highly sensitive dual-mode assay provided a linear range of 1.0-8.0 mU/mL, with detection limits of 0.34 mU/mL for the multicolor assay and 0.11 mU/mL for the photothermal assay. This method was successfully applied to the determination of ALP in serum samples.

Carbon Dots with Absorption Red-Shifting for Two-Photon Fluorescence Imaging of Tumor Tissue pH and Synergistic Phototherapy.

Phototherapy exhibits significant potential as a novel tumor treatment method, and the development of highly active photosensitizers and photothermal agents has drawn considerable attention. In this work, S and N atom co-doped carbon dots (S,N-CDs) with an absorption redshift effect were prepared by hydrothermal synthesis with lysine, o-phenylenediamine, and sulfuric acid as raw materials. The near-infrared (NIR) absorption features of the S,N-CDs resulted in two-photon (TP) emission, which has been used in TP fluorescence imaging of lysosomes and tumor tissue pH and real-time monitoring of apoptosis during tumor phototherapy, respectively. The obtained heteroatom co-doped CDs can be used not only as an NIR imaging probe but also as an effective photodynamic therapy/photothermal therapy (PDT/PTT) therapeutic agent. The efficiencies of different heteroatom-doped CDs in tumor treatment were compared. It was found that the S,N-CDs showed higher therapeutic efficiency than N-doped CDs, the efficiency of producing 1O2 was 27%, and the photothermal conversion efficiency reached 34.4%. The study provides new insight into the synthesis of carbon-based nanodrugs for synergistic phototherapy and accurate diagnosis of tumors.

A mitochondria-targeted ratiometric fluorescent nanoprobe for imaging of peroxynitrite in living cells.

Peroxynitrite (ONOO-) is a series of basic biological oxidants involved in physiological and pathological processes. The detection of ONOO- in biological systems has been challenging due to its extremely short half-life and low steady-state concentration. In this work, a ratiometric fluorescent nanoprobe for ONOO- was constructed by coupling covalently of graphene quantum dots (GQDs) with cyanine 5.5 (Cy5.5). This nanoprobe (GQD-Cy5.5) could selectively accumulate in mitochondrial, appears two strong fluorescence emission peaks at 520 and 694 nm. In the presence of ONOO-, the intensity of fluorescence emission peak at 520 nm increased and the intensity of fluorescence emission peak at 694 nm decreased. The ratio (F520 nm/F694 nm) of fluorescence intensity at two emission peaks had a good linear relationship with the concentration of ONOO- in the range of 0-6.0 µM, and the detection limit was 0.03 µM. The excellent properties of the nanoprobe enable its applications in the ratiometric fluorescence imaging of endogenous ONOO- in cell mitochondria.

A self-correcting fluorescent assay of tyrosinase based on Fe-MIL-88B-NH2 nanozyme.

A self-correcting fluorescent assay of tyrosinase (TYR) was developed by utilization of Fe-MIL-88B-NH2 as a peroxidase-like nanozyme and a capture probe. Fe-MIL-88B-NH2 nanozyme was selected as an electron donor, and the oxidization product (dopamine-o-quinone) acts as an energy acceptor. First, TYR catalyzes the oxidation of tyramine hydrochloride to dopamine and then to dopamine-o-quinone. Second, Fe-MIL-88B-NH2 with intrinsic peroxidase-like activity decomposes H2O2 to produce ·OH radicals, which further accelerate the oxidation of dopamine to dopamine-o-quinone. Excessive H2O2 and ·OH radicals reduce the interferences from ascorbic acid at the same time providing a self-correcting ability. Dopamine-o-quinone reacts with -NH2 groups on the ligand of Fe-MIL-88B-NH2 through Michael reaction which results in fluorescence quenching. Under 365-nm excitation, the fluorescence emission intensity at 452 nm gradually decreased with increasing TYR concentration varying from 0 to 10 U mL-1. The linear range is from 1 to 5 U mL-1 and the detection limit is 0.05679 U mL-1. This self-correcting fluorescent assay of tyrosinase exhibits good sensitivity and selectivity which is also successfully applied for tyrosinase inhibitor detection. Schematic representation of fluorescent assay for tyrosinase determination based on Fe-MIL-88B-NH2 nanozyme. A self-correcting fluorescent assay for tyrosinase was developed based on the Fe-MIL-88B-NH2 nanozyme.

Accelerating the peroxidase-like activity of MoSe2 nanosheets at physiological pH by dextran modification.

Surface modification of MoSe2via dextran during ultrasound exfoliation is demonstrated to be an efficient and easy strategy to accelerate the peroxidase-like catalytic activity of MoSe2 nanosheets at neutral pH. The enhancement of catalytic activity is owing to the rich negative charges of dextran on the dextran-modified MoSe2 nanosheets.

A competitive immunoassay for electrochemical impedimetric determination of chlorpyrifos using a nanogold-modified glassy carbon electrode based on enzymatic biocatalytic precipitation.

A direct competitive impedimetric immunoassay for chlorpyrifos (CPF) was developed that is based on the specific affinity of immunoassay and the enzymatic biocatalytic precipitation amplification strategy. The CPF antibody (anti-CPF) was anchored onto an electro-deposited nanogold modified glassy carbon electrode surface by adsorption of the Au-NH2 bond and Au-SH bond. This improved the electrode reactivity and the loading amount of anti-CPF. Abundant horseradish peroxidase (HRP) and bovine serum albumin-CPF (BSA-CPF) were anchored onto spherical gold nanoparticles (AuNPs, 16 ± 2 nm) to form HRP-AuNP-BSA-CPF (analyte competitor). CPF determination was achieved when the competitive immunoassay occurred between CPF and analyte competitor with anti-CPF. In the presence of H2O2 and 4-chloro-1-naphthol, an enzyme-mediated biocatalytic precipitation process was triggered and produced an insoluble 4-chloro-1(4H)-naphthalenone. This insoluble substance increased the Faradaic impedance of the base electrode. The impedimetric signal was determined at the formal potential of 220 mV and alternating voltage of 10 mV. This signal decreased with increasing concentration of CPF over a linear range of 1.0 × 10-3 ng mL-1~10 ng mL-1 with a detection limit of 0.070 pg mL-1. The immunoassay has been tested for determination of chlorpyrifos in complex matrices such as artificially spiked vegetables with recoveries in the range 85 to 110%. The relative standard deviations were less than 7.5%. Graphical abstractSchematic representation of electrochemical impedimetric immunoassay for chlorpyrifos determination before enzymatic biocatalytic precipitation (BCP, red line) process and after BCP process (blue line).