Ultrasensitive Electrochemical Biosensor Based on Efficient PDA-APDMAO Antifouling Interface and Dual-Signal Ratio Strategy for Trace Detection of Alpha-Fetoprotein in Human Serum.

In electrochemical analysis, developing biosensors that can resist the nonspecific adsorption of interfering biomolecules in human serum remains a huge challenge, which depends on the design of efficient antifouling materials. Herein, 3-aminopropyldimethylamine oxide (APDMAO) biomimetic zwitterions were prepared as antifouling interfaces. Among them, the unique positive and negative charges (N+-O-) of APDMAO promoted its hydrogen bonding with water molecules, forming a firm hydration barrier that endowed it with strong and stable antifouling performance. Meanwhile, its inherent amino groups could copolymerize with the biomimetic adhesive dopamine to form a thin layer of quinone intermediates, providing conditions for the subsequent binding of aptamers and signal probes. Importantly, the biomimetic APDMAO with functional groups and one-step oxidation characteristics solved the challenges of zwitterionic synthesis and modification, as well as improved biocompatibility of the sensing interface, thereby expanding the application potential of zwitterions as antifouling materials in sensing analysis. Thiol-containing alpha-fetoprotein (AFP) aptamers modified with methylene blue (MB) were coupled under controllable potential, greatly reducing the incubation time, which promoted the productization application of biosensors. In addition, the ratio sensing strategy using MB as internal standard factors and concanavalin-silver nanoparticles (ConA-Ag NPs) as signal probes was introduced to reduce background and instrument interferences, thus improving detection accuracy. On this basis, the proposed antifouling electrochemical biosensor achieved sensitive and accurate AFP detection over a wide dynamic range (10 fg/mL-10 ng/mL), with a low detection limit of 3.41 fg/mL (3σ/m). This work provides positive insights into the development of zwitterionic antifouling materials and clinical detection of liver cancer markers in human serum.

Antifouling Electrochemical Biosensor Based on the Designed Functional Peptide and the Electrodeposited Conducting Polymer for CTC Analysis in Human Blood.

Circulating tumor cells (CTCs) are considered reliable cancer biomarkers for the liquid biopsy of many types of tumors. The direct detection of CTCs in human blood with normal biosensors, however, remains challenging because of severe biofouling in blood that contains various proteins and a large number of cells. Herein, we report the construction of an antifouling electrochemical biosensor capable of assaying CTCs directly in blood, based on a designed multifunctional peptide and the electrodeposited conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The designed peptide possesses antifouling capability in complex biological media and specific recognition ability to capture breast cancer cells MCF-7. Meanwhile, electrodeposited PEDOT can promote electron transfer at the sensing interface, improve the signal-to-noise ratio for the detection, and thus enhance the sensitivity of the biosensor. The integration of the multifunctional peptide and conducting polymer PEDOT ensures that the developed biosensor is able to perform directly in blood samples without purification or separation. The antifouling electrochemical biosensor for the detection of MCF-7 cells exhibits a wide linear range over 4 orders, with a limit of detection (LOD) of 17 cells mL-1. More interestingly, even when performing in 25% human blood, the biosensor still retains a linear response with an LOD of 22 cells mL-1, without suffering significantly from biofouling in real blood. This work provides a promising strategy for the direct analysis of CTCs in human blood without a complicated pretreatment, and it may find practical application in the liquid biopsy of cancers.

Copolymer-Based Fluorescence Nanosensor for In Situ Imaging of Homocysteine in the Liver and Kidney of Diabetic Mice.

Homocysteine (Hcy) is one of the important biomarkers of clinical diagnosis, which is closely related to the occurrence and development of many diseases. Current analysis methods have difficulties in detecting Hcy in cells and living organisms. As a powerful technique, fluorescence methods combined the laser confocal imaging technology can achieve real-time visual tracking in cells and in vivo. Herein, we establish a conjugated copolymer-based fluorescence nanosensor (DPA-PFNP-Cu(II)) using the connected 2,7-dibromofluorene and 4,7-bis (2-bromothiophen-5-yl)-2-1-3-benzothiadiazole as the main chain. The competitive coordination between Hcy and Cu(II) allows the fluorescence of the polymer off to on. Finally, the nanosensor is applied for in situ imaging of Hcy levels in the kidney and liver of diabetic mice and is found that Hcy levels were positively correlated with the degree of diabetes. Notably, the depth of tissue penetration of the nanosensor enables Hcy detection of the liver and kidney through in vivo imaging without damage. Two-photon imaging and in vivo imaging achieve consistent results, which correct each other, improving the accuracy of the test result. The present works provide a new imaging technique for studying the occurrence and development of diabetes and screening of new drugs for treatment at the living level.

A novel self-powered aptasensor for digoxin monitoring based on the dual-photoelectrode membrane/mediator-free photofuel cell.

Self-powered sensor is considered as a promising, rapid, portable and miniaturized detection device that can work without external power input. In this work, a novel dual-photoelectrode self-powered aptasensor for digoxin detection was designed on the basis of a photofuel cell (PFC) composed of a black TiO2 (B-TiO2) photoanode and a CuBr photocathode in a single-chamber cell. The sensing platform avoided the use of membrane, free mediator, bioactive components and costly metal Pt electrodes. The large inherent bias between the Fermi energy level of B-TiO2 and that of CuBr improved the electricity output of PFC that the open circuit potential (OCP) and the maximum power density (Pmax) reached 0.58 V and 6.78 µW cm-2 respectively. Based on the excellent output of PFC, digoxin aptamer was immobilized on photoanode as the recognition element to capture digoxin molecules, which realized the high sensitive and selective detection of digoxin. The self-powered aptasensor displayed a broad linear in the range from 10-12 M to 10-5 M with a detection limit (3 S/N) of 0.33 pM. This work paved a luciferous way for further rapid, portable, miniaturized and on-site self-powered sensors.

Photo-triggered release of doxorubicin from liposomes formulated by amphiphilic phthalocyanines for combination therapy to enhance antitumor efficacy.

Multidrug combination therapy based on drug delivery systems (DDSs) has great potential for cancer treatment. Stimuli-sensitive DDSs further enhance therapeutic efficacy by providing controllable drug delivery. Herein, the phospholipid compound DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) was used to construct thermosensitive liposomes to load the photosensitizer ZnPc(PEG)4 (zinc phthalocyanine substituted by tetraethylene glycol) for molecular imaging, and photodynamic and photothermal therapy, together with doxorubicin (DOX) for chemotherapy. Interestingly, ZnPc(PEG)4 as an amphipathic molecule was found to be important in the construction of the liposomes, and it provided liposomes with improved stability. The thus-obtained liposomes ZnPc(PEG)4:DOX@LiPOs were demonstrated to have enhanced ROS production capacity, heat generation properties and a photo-triggered doxorubicin release effect, and, in cellular experiments, increased cytotoxicity and apoptotic cell proportions, compared to ZnPc(PEG)4@LiPOs and DOX@LiPOs. ZnPc(PEG)4 loaded in lipid bilayers showed stronger intracellular ROS production ability compared to free ZnPc(PEG)4. In vivo studies indicated that ZnPc(PEG)4:DOX@LiPOs exhibited enhanced tumor accumulation, increased anti-cancer effects and reduced liver retention. These photo-triggered liposomes constructed by the photosensitizer ZnPc(PEG)4 can also be used to package other cargo for combined target tumor therapy and molecular imaging.

Size-controlled DNA-cross-linked hydrogel coated silica nanoparticles served as a ratiometric fluorescent probe for the detection of adenosine triphosphate in living cells.

Herein, we have designed a ratiometric fluorescent nanoprobe for adenosine triphosphate sensing and imaging in living cells, based on silica nanoparticles and a DNA-functionalized hybrid hydrogel. This ratiometric detecting method could validly avoid false-positive signals. Due to its controllable size, favorable biocompatibility and biostability, the nanohydrogel exhibited high cellular permeability and fast response in living cells.

Fluorescent sensor array for separation-free dopamine analogue discrimination via polyethyleneimine-mediated self-polymerization reaction.

The effective discrimination of dopamine (DA) analogues is an enduring challenge because of their very tiny structural differences, and thus a separation technique is generally required during the conventional analysis. In this study, a hyperbranched polyethyleneimine (hPEI)-based fluorescent sensor array has been constructed for the separation-free and effective differentiation of four DA analogues. The discrimination includes two steps: firstly, the formation of fluorescent polymer nanoparticles (FPNs) with diverse emission profiles via hPEI-mediated self-polymerization reaction of DA analogues and secondly, the linear discriminant analysis of fluorescence patterns of the formed FPNs for the differentiation of DA analogues. The hPEI-assisted self-polymerization reaction of DA analogues and substitution group mediated optical properties of the resulted FPNs enable an excellent discrimination of four DA analogues at a concentration of 1.0 µM when linear discriminant analysis and hierarchical cluster analysis are smartly combined. Additionally, binary, tertiary and even quaternary mixtures of analogues can also be well distinguished with the proposed sensor array. The practicability of this established sensor array is validated by a high accuracy (100%) evaluation of 88 blind samples containing a single analogue or a mixture of two, three or four analogues.

A novel fluorescent biosensor for Adenosine Triphosphate detection based on the polydopamine nanospheres integrating with enzymatic recycling amplification.

Based on the protective performance of polydopamine nanospheres (PDANSs) for DNA against nuclease digestion and the specific recognition characteristic of aptamer, we have developed an enzymatic recycling signal amplification method for highly sensitive and selective detection of adenosine triphosphate (ATP). Fluorescence measurements were carried out to verify the DNA polymerase and exonuclease III (Exo III) assisted target recycling process and fluorescence signal amplification. In the absence of the ATP, initially, the signal DNA-PDANSs complex was in the "off" state due to the efficient fluorescence quenching of 6-carboxyfluorescein (FAM) adjacent to the surface of PDANSs. Due to the binding of the aptamer by ATP, it trigger DNA polymerase and Exo III assisted target recycling process by the product of release, the complex would change into the "on" state as a result of the dissociation of the FAM from the surface of PDANSs, thus providing greatly enhanced fluorescence emission intensity. The method allows quantitative detection of ATP in the range of 20-600nM with a detection limit of 8.32nM. This biosensor requires no complex operations, and is a new high efficiency method for ATP detection.

Enhanced chemiluminescence detection of glutathione based on isoluminol-PSM nanoparticles probe.

In this paper, a new chemiluminescence (CL) strategy was constructed for the determination of physiological thiols by using an isoluminol labeled nano-probe. The amino group on the surface of the magnetic beads (MBs) were converted into pyridyl disulfide groups by treatment with N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP), in the meantime, isoluminol and thiolated signal DNA were labeled on the surface of the polystyrene microspheres (PSMs). By treating the SPDP activated MBs with the modified PSMs, isoluminol molecules on the surface of the PSMs, along with the thiolated signal DNA, were attached to the surface of the MBs through disulfide bonds to form a CL probe. In the presence of glutathione (GSH), the disulfide bonds could be cleaved readily. The isoluminol molecules modified on the surface of the PSMs released from the CL probes were detached by magnetic separation and transferred to the dark closet for CL detection of isoluminol-H2O2-HRP system. Using GSH detection as a model, we prove a linear dose response in the range from 5 × 10(-10) to 8 × 10(-8)M. The detection limit of this trial for GSH determined is 5 × 10(-10)M. The proposed design was successfully applied to the extracts of K562 cell for intracellular thiols detection, the average amount of thiols was about 4.114 × 10(-13)M per K562 cell.