Target Deoxyribonucleic Acid-Recycled Lighting-Up Amplifiable Ratiometric Fluorescence Biosensing of Bicolor Silver Nanoclusters Hosted in a Switchable Deoxyribonucleic Acid Construct.

Ratiometric assays of label-free dual-signaling reporters with enzyme-free amplification are intriguing yet challenging. Herein, yellow- and red-silver nanocluster (yH-AgNC and rH-AgNC) acting as bicolor ratiometric emitters are guided to site-specifically cluster in two template signaling hairpins (yH and rH), respectively, and originally, both of them are almost non-fluorescent. The predesigned complement tethered in yH is recognizable to a DNA trigger (TOC) related to SARS-CoV-2. With the help of an enhancer strand (G15E) tethering G-rich bases (G15) and a linker strand (LS), a switchable DNA construct is assembled via their complementary hybridizing with yH and rH, in which the harbored yH-AgNC close to G15 is lighted-up. Upon introducing TOC, its affinity ligating with yH is further implemented to unfold rH and induce the DNA construct switching into closed conformation, causing TOC-repeatable recycling amplification through competitive strand displacement. Consequently, the harbored rH-AgNC is also placed adjacent to G15 for turning on its red fluorescence, while the yH-AgNC is retainable. As demonstrated, the intensity ratio dependent on varying TOC is reliable with high sensitivity down to 0.27 pM. By lighting-up dual-cluster emitters using one G15 enhancer, it would be promising to exploit a simpler ratiometric biosensing format for bioassays or clinical theranostics.

Modulating the Fluorescence of Silver Nanoclusters Wrapped in DNA Hairpin Loops via Confined Strand Displacement and Transient Concatenate Ligation for Amplifiable Biosensing.

It is intriguing to modulate the fluorescence emission of DNA-scaffolded silver nanoclusters (AgNCs) via confined strand displacement and transient concatenate ligation for amplifiable biosensing of a DNA segment related to SARS-CoV-2 (s2DNA). Herein, three stem-loop structural hairpins for signaling, recognizing, and assisting are designed to assemble a variant three-way DNA device (3WDD) with the aid of two linkers, in which orange-emitting AgNC (oAgNC) is stably clustered and populated in the closed loop of a hairpin reporter. The presence of s2DNA initiates the toehold-mediated strand displacement that is confined in this 3WDD for repeatable recycling amplification, outputting numerous hybrid DNA-duplex conformers that are implemented for a transient "head-tail-head" tandem ligation one by one. As a result, the oAgNC-hosted hairpin loops are quickly opened in loose coil motifs, bringing a significant fluorescence decay of multiple clusters dependent on s2DNA. Demonstrations and understanding of the tunable spectral performance of a hairpin loop-wrapped AgNC via switching 3WDD conformation would be highly beneficial to open a new avenue for applicable biosensing, bioanalysis, or clinical diagnostics.

Antibody-Responsive Ratiometric Fluorescence Biosensing of Biemissive Silver Nanoclusters Wrapped in Switchable DNA Tweezers.

Exploring the ratiometric fluorescence biosensing of DNA-templated biemissive silver nanoclusters (AgNCs) is significant in bioanalysis, yet the design of a stimuli-responsive DNA device is a challenge. Herein, using the anti-digoxin antibody (anti-Dig) with two identical binding sites as a model, a tweezer-like DNA architecture is assembled to populate fluorescent green- and red-AgNCs (g-AgNCs and r-AgNCs), aiming to produce a ratio signal via specific recognition of anti-Dig with two haptens (DigH). To this end, four DNA probes are programmed, including a reporter strand (RS) dually ended with a g-/r-AgNC template sequence, an enhancer strand (ES) tethering two same G-rich tails (G18), a capture strand (CS) labeled with DigH at two ends, and a help strand (HS). Initially, both g-AgNCs and r-AgNCs wrapped in the intact RS are nonfluorescent, whereas the base pairing between RS, ES, CS, and HS resulted in the construction of DNA mechanical tweezers with two symmetric arms hinged by a rigid "fulcrum", in which g-AgNCs are lighted up due to G18 proximity ("green-on"), and r-AgNCs away from G18 are still dark ("red-off"). When two DigHs in proximity recognize and bind anti-Dig, the conformation switch of these tweezers resultantly occurs, taking g-AgNCs away from G18 for "green-off" and bringing r-AgNCs close to G18 for "red-on". As such, the ratiometric fluorescence of r-AgNCs versus g-AgNCs is generated in response to anti-Dig, achieving reliable quantization with a limit of detection at the picomolar level. Based on the fast stimulated switch of unique DNA tweezers, our ratiometric strategy of dual-emitting AgNCs would provide a new avenue for a variety of bioassays.

Antibody-powered DNA switches to initiate the hybridization chain reaction for the amplified fluorescence immunoassay.

Designing antibody-powered DNA nanodevice switches is crucial and fascinating to perform a variety of functions in response to specific antibodies as regulatory inputs, achieving highly sensitive detection by integration with simple amplified methods. In this work, we report a unique DNA-based conformational switch, powered by a targeted anti-digoxin mouse monoclonal antibody (anti-Dig) as a model, to rationally initiate the hybridization chain reaction (HCR) for enzyme-free signal amplification. As a proof-of-concept, both a fluorophore Cy3-labeled reporter hairpin (RH) in the 3' terminus and a single-stranded helper DNA (HS) were individually hybridized with a recognition single-stranded DNA (RS) modified with Dig hapten, while the unpaired loop of RH was hybridized with the exposed 3'-toehold of HS, isothermally self-assembling an intermediate metastable DNA structure. The introduction of target anti-Dig drove the concurrent conjugation with two tethered Dig haptens, powering the directional switch of this DNA structure into a stable conformation. In this case, the unlocked 3'-stem of RH was implemented to unfold the 5'-stem of the BHQ-2-labeled quench hairpin (QH), rationally initiating the HCR between them by the overlapping complementary hybridization. As a result, numerous pairs of Cy3 and BHQ-2 in the formed long double helix were located in spatial proximity. In response to this, the significant quenching of the fluorescence intensity of Cy3 by BHQ-2 was dependent on the variable concentration of anti-Dig, achieving a highly sensitive quantification down to the picomolar level based on a simplified protocol integrated with enzyme-free amplification.

Fabrication of an iodide-selective electrode based on phthalocyaninatotitanium(IV) oxide and the selective determination of iodide in actual samples.

This work describes the development and fabrication of a selective polymeric membrane electrode for iodide ion based on a metallophthalocyanin complex with a titanium(IV) atom at the center (as an oxo-titanium, Ti=O, group), phthalocyaninatotitanium(IV) oxide (PcTiO), as a sensing carrier. The potential response characteristics of the electrode were investigated by changing the type of plasticizer as well as the amounts of the carrier and different lipophilic ionic site additives in the sensing membrane. It is shown that the membrane electrode incorporated with 2-nitrophenyl octyl ether as the plasticizer and hexadecyl trimethylammonium bromide as the appropriate cationic additive exhibits enhanced potential response toward iodide over other anions tested. Over the period of this study, the resulting electrode based on PcTiO displayed a stable near-Nernstian slope approaching -58.9 mV decade(-1) with a linear response spanning at least 5 orders of magnitude in concentration from 1.0 x 10(-1) to 9.2 x 10(-7) mol L(-1) and a detection limit of 8.5-10(-7) mol L(-1). The preferential potential response to iodide may be attributed to the unique recognition of carrier PcTiO in the organic membrane phase for iodide in solution. Under laboratory conditions, the present electrode also works well in partially nonaqueous media. The excellent analytical features of the proposed electrode could lead to its successful application in determining the end point in electrometric titration of iodide with Ag(+) and the direct potential determination of iodide concentration in wastewater and drug preparations.

The effects of dietary fatty acids on liver fatty acid composition and Delta(6)-desaturase expression differ with ambient salinities in Siganus canaliculatus.

Delta(6)-Desaturase (linoleoyl-CoA desaturase, EC 1.14.19.3) is the rate-limiting enzyme in the biosynthetic pathway of highly unsaturated fatty acid (HUFA). In this report, a Delta6 desaturase-like cDNA was cloned, and the relation of HUFA biosynthetic activity in liver with ambient salinity as well as dietary fatty acids was investigated in the euryhaline teleost Siganus canaliculatus. After the juveniles were fed four formulated diets (D1-D4) with different essential fatty acid composition (D1 with 23.49% HUFA, D2-D4 were HUFA-free, linoleic and alpha-linolenic acids account for 21.1% and 0.38%, 13.99% and 11.64%, 18.31% and 5.82% of the total fatty acids, respectively) for nine weeks, the growth performance showed no difference among groups in brackish water (10 ppt) or seawater (32 ppt) (P>0.05). Comparing liver fatty acids with fish fed D1, the content of arachidonic acid in fish fed D2 or D4 was significantly higher in 10 ppt (P<0.05), but showed no difference in 32 ppt; the contents of eicosapentaenoic (EPA), docosapentaenoic (DPA) and docosahexaenoic (DHA) acids in 10 ppt, as well as EPA in 32 ppt in fish fed D3 showed no difference, whereas those of DPA and DHA were significantly lower in 32 ppt (P<0.05). These data suggest that S. canaliculatus may convert linoleic and alpha-linolenic acids into HUFA and such a capacity was stronger in low salinity than that in high salinity. Consistent with this, the liver levels of Delta6 desaturase mRNA in fish fed D2-D4 were generally higher than in fish fed D1 in both salinities, and the total expression level in 10 ppt was about 1.56 times of that in 32 ppt, suggesting that transcriptional control of Delta6 desaturase is involved in such a HUFA biosynthesis. To our knowledge, this is the first report showing the relation of HUFA biosynthetic activity with ambient salinity in a euryhaline fish.

An electrochemiluminescent sensor based on functionalized conjugated polymer dots for the ultrasensitive detection of Cu2.

An ultrasensitive electrochemiluminescence (ECL) detection for Cu2+ was explored using the carboxyl functionalized poly(9,9-dioctylfluorenyl-2,7-diyl) (PS-COOH-co-PFO) dots as the signal label without adding any coreactant.

Highly selective iodide electrode based on the copper(II)-N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex.

In this paper, a new PVC-based liquid-membrane anion-selective electrode based on a copper(II) of N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex (Cu(II)BBAP) is described, which displays a preferential potentiometric response to iodide ion at pH 2.0 and an anti-Hofmeister selectivity sequence: I->SCN->ClO4->NO2->H2PO4->NO3->SO4(2-)>Br->Cl-. The electrode exhibits a near-Nernstian potential linear range of 8.2x10(-7)-1.0x10(-1) M with a detection limit of 5.3x10(-7) M and a slope of -58.8 mV per decade. The A.C. impedance technique and the UV/Vis spectroscopy technique were used to analyze the response mechanism. The electrode could be applied to determine iodide in medicine analysis, and the obtained results were fairly satisfactory.

A novel thiocyanate-selective electrode based on a zinc-phthalocyanine complex.

A novel thiocyanate (SCN-)-selective PVC membrane electrode based on a zinc-phthalocyanine (ZnPc) complex as neutral carrier is described. The membrane electrode containing ZnPc with 5.1% (w/w) ionophore, 29.2% (w/w) PVC, and 65.7% (w/w) 2-nitrophenyl octyl ether (o-NPOE) as plasticizer displayed an anti-Hofmeister selectivity sequence, SCN- > Sal- > I- > ClO4- > Br- > Cl- > NO3- > NO2- > H2PO4- > SO4(2-)), and exhibited near-Nernstian potential response to thiocyanate ranging from about 1.0 x 10(-1) to 1.0 x 10(-6) mol L(-1) with a detection limit of 7.5 x 10(-7) mol L(-1) and a slope of 58.1+/-0.5 mV per decade in pH 3.0 phosphate buffer solution at 25 degrees C. This preferential response is believed to be associated with the unique coordination between the central metal of the carrier and thiocyanate.