Distinguishable Magnetic Reporter Coordination with Buoyancy-Magnetism Separation for Immobilization-Free Dual-Target Electrochemical Immunosensing.

Simultaneous sensitive and precise determination of multibiomarkers is of great significance for improving detection efficiency, reducing diagnosis and treatment expenses, and elevating survival rates. However, the development of simple and portable biosensors for simultaneous determination of multiplexed targets in biological fluids still faces challenges. Herein, a unique and versatile immobilization-free dual-target electrochemical biosensing platform, which combines distinguishable magnetic signal reporters with buoyancy-magnetism separation, was designed and constructed for simultaneous detection of carcinoembryonic (CEA) and α-fetoprotein (AFP) in intricate biological fluids. To construct such distinguishable magnetic signal reporters with signal transduction, amplification, and output, secondary antibodies of CEA and AFP were respectively functionalized on methylene blue (MB) and 6-(ferrocenyl)hexanethiol (FeC) modified Fe3O4@Au magnetic nanocomposites. Meanwhile, a multifunctional flotation probe with dual target recognition, capture, and isolation capability was prepared by conjugating primary antibodies (Ab1-CEA, Ab1-AFP) to hollow buoyant microspheres. The target antigens of CEA and AFP can trigger a flotation-mediated sandwich-type immunoreaction and capture a certain amount of the distinguishable magnetic signal reporter, which enables the conversion of the target CEA and AFP quantities to the signal of the potential-resolved MB and FeC. Thus, the MB and FeC currents of magnetically adsorbed distinguishable magnetic reporters can be used to determine the CEA and AFP targets simultaneously and precisely. Accordingly, the proposed strategy exhibited a delightful linear response for CEA and AFP in the range of 100 fg·mL-1-100 ng·mL-1 with detection limits of 33.34 and 17.02 fg·mL-1 (S/N = 3), respectively. Meanwhile, no significant nonspecific adsorption and cross-talk were observed. The biosensing platform has shown satisfactory performance in the determination of real clinical samples. More importantly, the proposed approach can be conveniently extended to universal detection just by simply substituting biorecognition events. Thus, this work opens up a new promising perspective for dual and even multiple targets and offers promising potential applications in clinical diagnosis.

Fascinating Immobilization-Free Electrochemical Immunosensing Strategy Based on the Cooperation of Buoyancy and Magnetism.

Rapid and accurate detection of biomolecules is of vital importance for the diagnosis of disease and for performing timely treatments. The point-of-care analysis of cancer biomarkers in the blood with low cost and easy processing is still challenging. Herein, an advanced and robust strategy, which integrates the buoyant recognition probe with the magnetic reporter probe in one solution, was first proposed for immobilization-free electrochemical immunosensing. The tumor marker of alpha fetoprotein (AFP) can be captured immune-buoyantly, and then a multifunctional magnetic reporter probe in pseudo-homogeneous solution was further captured to fulfill a sandwich-type immunoreaction. The residual magnetic reporter probe can be firmly and efficiently attracted on a magnetic glassy carbon electrode to fulfill the conversion of the target AFP amount into the residual magnetic electrochemical signal indicator. As a result, the electrochemical signal of methylene blue can accurately reflect the original level of target antigen AFP concentration. By integrating buoyancy-driven quasi-homogenous biorecognition with magnetism-mediated amplification and signal output, the proposed immobilization-free electrochemical immunosensing strategy displayed a wide range of linear response (100 fg mL-1 to 10 ng mL-1), low detection limit (14.52 fg mL-1), and good reproducibility, selectivity, and stability. The designed strategy manifests remarkable advantages including assay simplicity, rapidness, and high sensitivity owing to the in-solution instead of on-electrode biorecognition that could accelerate and improve the biorecognition efficiency. To the best of our knowledge, this is the first cooperation of buoyancy-driven biorecognition with magnetism-mediated signal output in bioanalysis, which would be attractive for rapid clinic biomedical application. Thus, this work provides a fresh perspective for convenient and favorable immobilization-free electrochemical biosensing of universal biomolecules.

Ratiometric Electrochemiluminescence Sensing of Carcinoembryonic Antigen Based on Luminol.

Ratiometric electrochemiluminescence (ECL) sensors can efficiently remove environmental interference to attain precise detection. Nonetheless, two eligible luminophores or coreactants were usually needed, increasing the complexity and restricting their practical application. In this study, a single luminophore of luminol with a single coreactant of H2O2 was employed to construct a dual-potential ratiometric ECL sensor for the detection of carcinoembryonic antigen (CEA). The produced palladium nanoclusters (Pd NCs) employing a DNA duplex as a template could not only stimulate luminol to produce cathodic ECL (Icathodic) but also quench its anodic ECL (Ianodic). During the detection process, CEA could damage the double-stranded structure and reduce the Pd NCs' amount, triggering a significant decrease in the ratio of Icathodic to Ianodic (Icathodic/Ianodic) and thereby achieving sensitive CEA's detection. Furthermore, the Icathodic/Ianodic was independent of the H2O2 concentration, which avoided a prejudicial effect from H2O2 decomposition and considerably enhanced the detection's reliability. The developed ratiometric ECL sensor demonstrated a sensitive detection toward CEA with a wide linear range from 100 ag/mL to 10 ng/mL and a detection limit of 87.1 ag/mL (S/N = 3). In conclusion, this study offers a new idea for constructing ratiometric ECL sensors based on a single luminophore and technical support for cancer's early diagnosis.

Thermally Hypsochromic or Bathochromic Emissions? The Silver Nuclei Does Matter.

Structural modulation of core-shell silver nanoclusters from the inside is a huge challenge but of great importance in their syntheses. Herein, two silver nanoclusters [Ag3 S9 @Ag42 ] (SD/Ag45b) and [Ag9 S9 @Ag42 ] (SD/Ag51a) are isolated in the presence of different kinds of sulfonic acids. Uniquely, SD/Ag45b and SD/Ag51a show typical core-shell structures with the similar Ag42 shell but different cores. The outer shell of 42 silver atoms comprises two Ag3 trigons at two poles encircled by three equatorial distorted square cupolas (J4 , Ag12 ). The core in SD/Ag45b is a silver trigon ligated by nine S2- ions (Ag3 S9 ), while a tricapped triangular prismatic Ag9 also ligated by the same amount of S2- ions (Ag9 S9 ) is observed in the inner core of SD/Ag51a. The electrospray ionization mass spectrometry (ESI-MS) indicates that the introduction of p-toluenesulfonic acid can realize the transformation from SD/Ag45b to Ag51 . SD/Ag45b and SD/Ag51a show inverse luminescence thermochromic behaviors in the near-infrared (NIR) region, mainly dictated by the inner silver cores. This work not only realizes the synthesis of new silver nanoclusters by core modulation but also provides a prototype to get molecular-level insight into the correlation between structure and luminescence thermochromism.

A novel ratiometric electrochemical biosensing strategy based on T7 exonuclease-assisted homogenous target recycling coupling hairpin assembly-triggered double-signal output for the multiple amplified detection of miRNA.

A novel ratiometric electrochemical biosensing strategy based on T7 exonuclease (T7 Exo)-assisted homogenous target recycling coupling hairpin assembly triggered dual-signal output was proposed for the accurate and sensitive detection of microRNA-141 (miRNA-141). Concretely, in the presence of target miRNA, abundant signal transduction probes were released via the T7 Exo-assisted homogenous target recycling amplification, which could be captured by the specially designed ferrocene-labeled hairpin probe (Fc-H1) on -electrode interface and triggered the nonenzymatic catalytic hairpin assembly (Fc-H1 + MB-H2) to realize the cascade signal amplification and dual-signal output. Through such a conformational change process, the electrochemical signal of Fc (IFc) and MB (IMB) is proportionally and substantially decreased and increased. Therefore, the signal ratio of IMB/IFc can be employed to accurately reflect the true level of original miRNA. Benefiting from the efficient integration of the T7 Exo-assisted target recycle, nonenzymatic hairpin assembly and dual-signal output mode, the proposed sensor could realize the amplified detection of miRNA-141 effectively with a wide detection range from 1 fM to 100 pM, and a detection limit of 200 aM. Furthermore, it exhibits outstanding sequence specificity to discriminate mismatched RNA, acceptable reproducibility and feasibility for real sample. This strategy effectively integrated the advantages of multiple amplification and ratiometric output modes, which could provide an accurate and efficient method in biosensing and clinical diagnosis.

Graphene-PtPd nanocomposite for low-potential-driven electrochemiluminescent determination of carcinoembryonic antigen using Ru(bpy)32.

As well known, the electrochemiluminescence (ECL) of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) heavily relies on highly positive or negative triggered voltage, prejudicing the detection toward the bio-molecules. In this work, Ru(bpy)32+ could generate enhanced and stable ECL at a low potential of 0.05 V (vs. Ag/AgCl) on graphene-PtPd hybrid, attributing to its excellent electrocatalysis from the synergistic effect between Pt and Pd. The obtained low-potential-driven ECL could be quenched by MoS2 nanoflowers. Based on the quenching effect, a sandwich "signal-off" ECL immunosensor was fabricated to sensitively detect carcinoembryonic antigen (CEA). A linear calibration curve from 1 fg mL-1 to 1 ng mL-1 was obtained along with a low detection limit of 0.54 fg mL-1 (S/N = 3) under optimal conditions. The sensor showed satisfactory specificity, stability, and reproducibility and was successfully applied to determine CEA in actual samples. The recoveries ranged from 98.80 to 100.23%, and the relative standard deviation (RSD) was lower than 5%. Above all, this work explored new materials in low-potential-driven ECL system and provided a reliable sensing strategy for clinical applications.

Dual-potential ratiometric electrochemiluminescence based on single emitter and single coreactant for the sensitive detection of carcinoembryonic antigen.

Dual-potential ratiometric electrochemiluminescence (ECL) is in favor of resistance to environmental interference. However, two kinds of emitters or coreactants, and a wide scan potential range (>2 V) are mandatory. This work developed a new dual-potential ratiometric ECL sensor for detection of carcinoembryonic antigen (CEA) using single emitter (luminol) and single coreactant (H2O2) with a mild potential range from -0.1 to 0.6 V. Luminol could produce a strong cathodic ECL (Ec) induced by hydroxyl radicals (HO‧) from the reduction of H2O2, and a relatively weak anodic ECL (Ea). After the ferrocene modified CEA aptamer (Apt-Fc) was attached, Fc could promote Ea by catalyzing the oxidation of H2O2, and reduce Ec by consuming HO‧. With the cycling amplification of the exonuclease I, CEA could substantially reduce the amount of Apt-Fc, resulting in the decrease of Ea and the rise of Ec. So, the ratio of Ec to Ea (Ec/Ea) was used as the detection signal, realizing the sensitive determination of CEA from 0.1 pg mL-1 to 10 ng mL-1 with a LOD of 41.85 fg mL-1 (S/N = 3). The developed sensor demonstrated excellent specificity, stability and reproducibility, with satisfactory results in practical detection.

An electrochemical ratiometric biosensor for the detection of dopamine based on an MXene-Au nanocomposite.

Compared with single signal detection, a ratiometric biosensor could offer more accurate and reliable results. Here, a ratiometric electrochemical biosensor for the sensitive and accurate detection of dopamine was developed based on the strong adsorption ability of MXene-Au toward methylene blue, an inner reference element. This ratiometric sensing strategy opened up a new avenue for the development of a ratiometric platform.

Electrochemiluminescence detection of miRNA-21 based on dual signal amplification strategies: Duplex-specific nuclease -mediated target recycle and nicking endonuclease-driven 3D DNA nanomachine.

DNA nanomachines have shown potential application in the construction of various biosensors. Here, an electrochemiluminescence biosensor for the sensitive detection of miRNA-21 were reported based on three-dimensional (3D) DNA nanomachine and duplex-specific nuclease (DSN)-mediated target recycle amplification strategy. First, the bipedal DNA walkers were obtained by DSN-mediated digestion reaction initiated by target miRNA-21.3D DNA tracks were prepared by modifying Fe3O4 magnetic beads (MBs) with ferrocene-labeled DNA (Fc-DNA). The produced DNA walkers autonomously moved along 3D DNA tracks powered by nicking endonuclease. During the movement, ferrocene-labeled DNA was cleaved, resulting in large amounts of Fc-labeled DNA fragments away from the MBs surface. Finally, the liberated Fc-labeled DNA fragments were dropped on the C-g-C3N4 modified electrode surface, leading to the quenching of C-g-C3N4 electrochemiluminescence (ECL). Benefiting from the dual amplification strategy of 3D DNA nanomachine and DSN-mediated target recycling, the developed ECL biosensor exhibited an excellent performance for miRNA-21 detection with a wide linear range of 10 fM to 10 nM and a low detection limit of 1.0 fM. This work offers a new thought for the application of DNA walkers in the construction of various biosensors.

The effect of ultra-high pretreatment on free, esterified and insoluble-bound phenolics from mango leaves and their antioxidant and cytoprotective activities.

Ultra-high pressure (UHP) is a novel non-thermal pretreatment method in food processing for improving the extraction yield of polyphenols and functional properties. The present work investigated the phenolic profiles, antioxidant activities, and cytoprotective effects of the free, esterified, and insoluble-bound phenolic fractions from mango leaves before and after ultra-high pressure (UHP) treatment. UHPLC-Q-Orbitrap-MS/MS analysis resulted in the identification of 42 phenolic compounds in the different phenolic forms. UHP pretreatment could significantly influence the contents of total phenols, total flavonoids and individual compounds in the different phenolic fractions (p < 0.05). After UHP pretreatment, these phenolic fractions exhibited greater antioxidant activity, and inhibited reactive oxygen species production and cell apoptosis (p < 0.05). Meanwhile, IBP were the most potential antioxidative and cytoprotective ingredients. Therefore, UHP pretreated mango leaves with enhanced bioactivity could be used as biological agents in the health food industry to improve its application and economic values.

Revealing the chirality origin and homochirality crystallization of Ag14 nanocluster at the molecular level.

Although chirality is an ever-present characteristic in biology and some artificial molecules, controlling the chirality and demystifying the chirality origin of complex assemblies remain challenging. Herein, we report two homochiral Ag14 nanoclusters with inherent chirality originated from identical rotation of six square faces on a Ag8 cube driven by intra-cluster π···π stacking interaction between pntp- (Hpntp = p-nitrothiophenol) ligands. The spontaneous resolution of the racemic (SD/rac-Ag14a) to homochiral nanoclusters (SD/L-Ag14 and SD/R-Ag14) can be realized by re-crystallizing SD/rac-Ag14a in acetonitrile, which promotes the homochiral crystallization in solid state by forming C-H···O/N hydrogen bonds with nitro oxygen atoms in pntp- or aromatic hydrogen atoms in dpph (dpph = 1,6-bis(diphenylphosphino)hexane) on Ag14 nanocluster. This work not only provides strategic guidance for the syntheses of chiral silver nanoclusters in an all-achiral environment, but also deciphers the origin of chirality at molecular level by identifying the special effects of intra- and inter-cluster supramolecular interactions.

Construction of aptasensors for sensitive detection of 8-OH-dG based on a diffusion mediated electrochemiluminescence quenching effect.

A DNA immobilization-free ECL aptasensor was developed for the detection of 8-hydroxy-2'-deoxygunosine based on the diffusion mediated ECL quenching effect. This ECL aptasensor exhibited a high sensitivity and low detection limit by combining homogeneous DNA reaction with dual signal amplifications: target-induced multi-DNA release and Exo I-assisted target recycling.

A sensitive electrochemical aptasensor for Mucin 1 detection based on catalytic hairpin assembly coupled with PtPdNPs peroxidase-like activity.

In this work, an ultrasensitive aptasensor for the detection of Mucin 1 (MUC1) was presented based on the target-induced catalytic hairpin assembly combined with excellent mimic peroxidase performance of PtPd bimetallic nanoparticles (PtPdNPs). Traditionally, the cyclic reuse of target protein was achieved by protein conversion with enzyme cleavage or polymerization, which is costly and complex. However, in this work, it can be performed by simple strand displacement. In addition, PtPdNPs, a mimic peroxidase, was used a probe to catalyze the oxidation of tetramethylbenzidine (TMB) by H2O2, leading to the electrochemical signal amplification. With this ingenious design, the prepared aptasensor for MUC1 detection showed a favorable linear response from 100 fg mL-1 to 1 ng mL-1 and a relatively low detection limit of 16 fg mL-1. The proposed biosensor possessed acceptable stability, selectivity and reproducibility for MUC1 assay. Additionally, the fabricated aptasensor has been successfully applied to detect MUC1 in serum samples with satisfactory results. This new strategy supplied one efficient approach to improve signal amplification, which also open an avenue for sensitivity enhancement in targets detection.

Ultrasensitive electrochemiluminescence aptasensor for 8-hydroxy-2'-deoxyguanosine detection based on target-induced multi-DNA release and nicking enzyme amplification strategy.

8-Hydroxy-2'-deoxyguanosine (8-OH-dG) is a principal stable marker of DNA oxidative damage. Sensitive and specific detection of 8-OH-dG is of great importance for early disease diagnosis. In this paper, we developed an electrochemiluminescence aptasensor for 8-OH-dG detection based on target induced multi-DNA release and nicking enzyme signaling amplification strategy. First, three kinds of short DNAs were aligned on the aptamers immobilized on the magnetic beads. In the presence of 8-OH-dG, the aptamer recognized and specifically bound with 8-OH-dG, leading to the release of three kinds of short DNAs and three-fold signal amplification. Then the released short DNAs hybridized with ferrocence (Fc) labeled hairpin DNA (Fc-HP) immobilized on the gold electrode to form a double strand DNA. Subsequently, nicking endonuclease (Nt.AlwI) recognized the asymmetric sequence in the dsDNA and cleaved the substrate strand (Fc-HP) into two parts, one fragments containing Fc would leave the surface of electrode. Based on the quenching effect of Fc on the electrochemiluminescence (ECL) of Ru(bpy)32+/TPA, a signal-on ECL aptasensor was developed. At the same time, three kinds of short DNAs were released again and reused to initiate the repeated cycles of hybridization-cleavage. Under double signal amplification, this aptasensor achieved a low detection of 25 fM and a wide linear range from 100 fM to 10 nM for 8-OH-dG. Besides, the amount of 8-OH-dG in urine samples derived from different people were determined with satisfactory results.

An electrochemical aptasensor for the highly sensitive detection of 8-hydroxy-2'-deoxyguanosine based on the hybridization chain reaction.

In the present work a highly sensitive and selective aptasensor was developed for the determination of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) based on the hybridization chain reaction (HCR) signal amplification. It was observed that the aptamer of 8-OH-dG could hybridize with the capture DNA immobilized on the gold electrode with a sticky tail left, which initiated the HCR and led to the formation of extended dsDNA structure on the electrode surface. Then the electroactive species ([Ru(NH3)6]3+, RuHex) intercalated into the dsDNA grooves to generate the amplified signal. However, in the presence of 8-OH-dG, the aptamer containing G-rich nucleic acid sequences would be induced to form a G-quadruplex structure, which made it impossible to continue the HCR. So the detection signal will significantly decrease. Under the optimal conditions, the peak current of RuHex was linear with the logarithm of 8-OH-dG concentration in the range from 10pM to 100µM with the detection limit of 2.5pM. By integrating the merits of enzyme-free amplification power of the HCR and the inherent high sensitivity of the electrochemical technique, the prepared aptasensor not only showed high sensitivity for the detection of 8-OH-dG, but also exhibited good selectivity against to the uric acid, an important interferent in the urine sample. Particularly, the aptasensor was applied to detect 8-OH-dG in urine samples with satisfactory results.

A versatile label-free electrochemical biosensor for circulating tumor DNA based on dual enzyme assisted multiple amplification strategy.

A versatile label-free electrochemical biosensor based on dual enzyme assisted multiple amplification strategy was developed for ultrasensitive detection of circulating tumor DNA (ctDNA). The biosensor consists of a triple-helix molecular switch (THMS) as molecular recognition and signal transduction probe, ribonuclease HII (RNase HII) and terminal deoxynucleotidyl transferase (TdT) as dual enzyme assisted multiple amplification accelerator. The presence of target ctDNA could open THMS and trigger RNase HII-assisted homogenous target recycling amplification to produce substantial signal transduction probe (STP). The released STP hybridized with the capture probe immobilized on a gold electrode, then TdT and assistant probe were further employed to fulfill TdT-mediated cascade extension and generate stable DNA dendritic nanostructures. The electroactive methyl blue (MB) was finally used as the signal reporter to realize the multiple electrochemical amplification ctDNA detection as the amount of MB is positively correlated with the target ctDNA. Combined with the efficient recognition capacity of the designed THMS and the excellent multiple amplification ability of RNase HII and TdT, the constructed sensing platform could detect KRAS G12DM with a wide detection range from 0.01 fM to 1 pM, and the limit of detection as low as 2.4 aM. Besides, the platform is capable of detecting ctDNA in biological fluid such as plasma. More importantly, by substituting the loop of THMS with different sequences, this strategy could be conveniently expanded into the detection of other ctDNA, showing promising potential applications in clinical cancer screening and prognosis.

A Label-Free and Sensitive Fluorescent Qualitative Assay for Bisphenol A Based on Rolling Circle Amplification/Exonuclease III-Combined Cascade Amplification.

Bisphenol A (BPA) detection in drinking water and food packaging materials has attracted much attention since the discovery that BPA can interfere with normal physiological processes and cause adverse health effects. Here, we constructed a label-free aptamer fluorescent assay for selective and sensitive detection of BPA based on the rolling circle amplification (RCA)/Exonuclease III (Exo III)-combined cascade amplification strategy. First, the duplex DNA probe (RP) with anti-BPA aptamer and trigger sequence was designed for BPA recognition and signal amplification. Next, under the action of BPA, the trigger probe was liberated from RP to initiate RCA reaction as primary amplification. Subsequently, the RCA products were used to trigger Exo III assisted secondary amplification with the help of hairpin probes, producing plenty of "G-quadruplex" in lantern-like structures. Finally, the continuously enriched "G-quadruplex lanterns" were lightened by zinc(II)-protoporphyrin IX (ZnPPIX) generating enhanced fluorescence signals. By integrating the primary RCA and secondary Exo III mediated cascade amplification strategy, this method displayed an excellent sensitivity with the detection limits of 5.4 × 10-17 M. In addition, the anti-BPA aptamer exhibits high recognition ability with BPA, guaranteeing the specificity of detection. The reporter signal probe (G-quadruplex with ZnPPIX) provides a label-free fluorescence signals readout without complicated labeling procedures, making the method simple in design and cost-effective in operation. Moreover, environmental samples analysis was also performed, suggesting that our strategy was reliable and had a great potential application in environmental monitoring.