Cobalt Oxyhydroxide Nanosheets Research Articles

Spatial and electronic effects synergistically enhanced electrocatalytic oxygen evolution using atomic iridium-anchored cobalt oxyhydroxide nanosheets

Single-atom catalysts (SACs) based on noble metals play irreplaceable roles in the field of catalysis but unfortunately suffer from spatial constraints ranging from either lattice substitution, atomic dilution, or in-layer immobilization. Herein, this work was designed to overcome the limitation by locating discrete dangling coordinatively unsaturated [IrO5] motif atop γ-phase cobalt oxyhydroxide (γ-CoOOH) nanosheets to create a spatially novel catalyst (Ir1/CoOOHsur). For comparison, the lattice-doped catalyst (Ir1/CoOOHlat) was also synthesized via substituting Co in γ-CoOOH by Ir single atoms. The distinct location arrangements of Ir single atoms generated two different active sites that both weakened the adsorption of oxygenated intermediates relative to γ-CoOOH due to the upshifted O 2p-band center. Moreover, Ir1/CoOOHsur displayed a much weaker adsorption capability (closer to an ideal catalyst) than Ir1/CoOOHlat. Therefore, the spatial and electronic effects of discrete dangling [IrO5] motifs atop Ir1/CoOOHsur synergistically optimized the adsorption of oxygenated intermediates and thus gained the lowest energy barrier of the rate-determining step for oxygen evolution reaction. When used as the cathode catalyst in rechargeable zinc-air batteries, Ir1/CoOOHsur exhibited higher power density (101 mW cm−2) and cycling durability (800 h) than IrO2 (94 mW cm−2, 50 h). This study broadens noble metal-based SACs analogues and offers appealing opportunity to design target catalysts with the synergism of spatial and electronic effects for diverse catalytic applications.

CRISPR/Cas12a-based fluorescence aptasensor integrated with two-dimensional cobalt oxyhydroxide nanosheets for IFN-γ detection

Cytokine storm (CS) is a risky immune overreaction accompanied by significant elevations of pro-inflammatory cytokines including interferon-γ (IFN-γ), interleukin and tumor necrosis factor. Sensitive detection of cytokine is conducive to studying CS progress and diagnosing infectious diseases. In this study, we developed a tandem system combining aptamer, strand displacement amplification (SDA), CRISPR/Cas12a, and cobalt oxyhydroxide nanosheets (termed Apt-SCN tandem system) as a signal-amplified platform for IFN-γ detection. Owing to the stronger affinity, target IFN-γ bound specifically to the aptamer from aptamer-complementary DNA (Apt-cDNA) duplex. The cDNA released from the Apt-cDNA duplex initiated SDA, resulting in the generation of double-stranded DNA products that could activate the trans-cleavage activity of CRISPR/Cas12a. The activated CRISPR/Cas12a further cleaved FAM-labeled single-stranded DNA probe, preventing it from adhering to the cobalt oxyhydroxide nanosheets and recovering the fluorescence signal. Sensitive fluorometric analysis of IFN-γ was successfully performed with detection limit as low as 0.37 nM. Unlike traditional protein analysis methods, Apt-SCN tandem system incorporates multiple signal amplification techniques and may also be applicable for other cytokines assay. This study was the initial study to utilize SDA and CRISPR/Cas12a to detect IFN-γ, showing great potential for cytokines clinical assay and CS prevention.

CoOOH nanosheets ensure ratiometric fluorescence assay of acetylcholinesterase

Cobalt oxyhydroxide nanosheets (CoOOH) with peroxidase-like activity provide a promising probe for acetylcholinesterase (AChE) sensing through a ratiometric fluorescence strategy. Fluorescence of silicon quantum dots (SiQDs) at 457 nm was quenched by CoOOH on account of inner-filter effect (IFE). Meanwhile, the nonfluorescent o-phenylenediamine (OPD) was catalytically oxidized to 2,3-diaminophenazine (oxOPD) by CoOOH nanosheets with emission at 572 nm. The acetylcholine (ATCh) was catalytically hydrolyzed by AChE to enzymatic thiocholine (TCh), which decomposed CoOOH to Co2+, recovered the fluorescence of SiQDs and reduced the emission of oxOPD. Fluorescence ratio at F457/F572 serves as signal output for AChE detection within 5 × 10−5–0.05 and 0.05–10 U mL−1, with a limit of detection (LOD) of 3.2 × 10−5 U mL−1. The sensing strategy was applied for AChE assay in human blood and erythrocyte.

Determination of prostate-specific antigen via the assembly of a two-dimensional nanoplatform

Two-dimensional platforms generate considerable interests due to diverse application. We report a “turn-on” fluorescent nanoprobe for prostate-specific antigen (PSA) detection. It is based on cobalt oxyhydroxide nanosheets (CoOOH NSs). Fluorescein amidite (abbreviated as FAM)-labeled aptamer probe (abbreviated as FAM-aptamer) has been adsorbed onto the nanosheets. Energy transfer between substrate and optical species has induced the quenching of FAM-aptamer emission. The strong affinity of FAM-aptamer to the target PSA causes the formation of a rigid aptamer structure. The integration between FAM-aptamer and CoOOH NSs has been drastically affected. The release of the aptamer probe from the nanosheet surface has been realized. The green luminescence has been recovered. The dynamic nanosensor exhibits highly sensitive performance toward PSA with a linear detection range from 0.1 to 5 ng/mL. Its detection limit is measured to be 56.1 pg/mL. Therefore, a simple and efficient sensing platform for the detection of prostate cancer can be established.

Alcohols electrooxidation coupled with H2 production at high current densities promoted by a cooperative catalyst

Electrochemical alcohols oxidation offers a promising approach to produce valuable chemicals and facilitate coupled H2 production. However, the corresponding current density is very low at moderate cell potential that substantially limits the overall productivity. Here we report the electrooxidation of benzyl alcohol coupled with H2 production at high current density (540 mA cm−2 at 1.5 V vs. RHE) over a cooperative catalyst of Au nanoparticles supported on cobalt oxyhydroxide nanosheets (Au/CoOOH). The absolute current can further reach 4.8 A at 2.0 V in a more realistic two-electrode membrane-free flow electrolyzer. Experimental combined with theoretical results indicate that the benzyl alcohol can be enriched at Au/CoOOH interface and oxidized by the electrophilic oxygen species (OH*) generated on CoOOH, leading to higher activity than pure Au. Based on the finding that the catalyst can be reversibly oxidized/reduced at anodic potential/open circuit, we design an intermittent potential (IP) strategy for long-term alcohol electrooxidation that achieves high current density (>250 mA cm−2) over 24 h with promoted productivity and decreased energy consumption.

Surface recognition strategy via ascorbic acid-triggered decomposition of boron nitride-loaded cobalt oxyhydroxide nanosheets

As for the accurate determination of analytes, most of chemical probes suffer from poor selectivity and data fluctuation. Sensor systems via colorimetric and fluorometric modes have caused considerable interests since the two ways are free from employment of special instrumentation and complicated techniques. A new type of cobalt oxyhydroxide (CoOOH) nanosheet has been developed and boron nitride is incorporated. Such nanoplatform can oxidize o-phenylenediamine (OPD) to 2,3-diaminophenazine (OxOPD) with emission change. In the presence of ascorbic acid, CoOOH can be reduced to Co2+ ions and the generation of OxOPD has been suppressed. Therefore, the fluorescent signal of boron nitride has been recovered and ratiometric determination for ascorbic acid can be realized (detection limit: 1.07 μM; linear range: 0.05–80 μM). In addition, colorless 3,3′,5,5′-tetramethylbenzidine (TMB) can be transformed into oxidized form-TMBox with blue color and the sensitivity can reach as low as 120 nM. Current study will not only provide a typical case of colorimetric and fluorometric sensing for quantitative analysis of ascorbic acid, but also promote a new molecular design concept in practical field.

A novel sandwich-like cytosensor based on aptamers-modified magnetic beads and carbon dots/cobalt oxyhydroxide nanosheets for circulating tumor cells detection

Abstract As a part of fluid biopsy, circulating tumor cells (CTCs) contain enormous tumor information, so the detection of CTCs is very helpful in clinical diagnosis and therapy. Here, we applied aptamers-modified magnetic beads (Apt@MBs) and carbon dots/cobalt oxyhydroxide nanosheets systems (CDs/CoOOH) to develop a new cytosensor for ultrasensitive and specific detection of CTCs. At first, amino-modified magnetic beads (MBs) were cross-linked with carboxyl-modified MUC1 aptamers (Apt) to gain Apt@MBs. Then, folic acid (FA) functionalized carbon dots (FA@CDs) were assembled onto cobalt oxyhydroxide nanosheets (CoOOH) to obtain FA@CDs/CoOOH with fluorescence quenching. In the detection systems, Apt@MBs identified and accumulated MCF-7 cells, forming Apt@MBs/MCF-7 cells, which then combined with FA@CDs/CoOOH to obtain sandwich-like Apt@MBs/MCF-7 cells/FA@CDs/CoOOH. Finally, ascorbic acid (AA) decomposed CoOOH to release carbon dots (CDs), and the fluorescence of abundant CDs act as efficient signal output. The cytosensor detected MCF-7 cells with a wide dynamic range (10 ∼ 105 cells/mL) and a low limit of detection (5 cells/mL), owing to the specific identification and effective enrichment of Apt@MBs as well as anti-interference capability and signal amplification of FA@CDs/CoOOH. Most importantly, the cytosensor successfully discriminated MCF-7 cells from white blood cells, exhibiting potentiality in ultrasensitive CTCs detection in clinical diagnosis.

Construction of cobalt oxyhydroxide nanosheets with rich oxygen vacancies as high-performance lithium-ion battery anodes

Hierarchical nanoporous cobalt oxyhydroxide (CoOOH) nanosheets are prepared for use as an anode material in high energy density lithium-ion batteries.

2D CoOOH nanosheets as oxidase mimic for the colorimetric assay of sulfite in food

Here, we report a rapid, sensitive and selective colorimetric assay for sulfite (SO32-) based on the intrinsic oxidase-like activity of 2D cobalt oxyhydroxide nanosheets (CoOOH NSs). The 2D CoOOH nanozyme could directly oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into blue products (TMBox) in an aerobic solution without H2O2. Interestingly, the presence of SO32- could effectively inhibit the CoOOH NS-O2-TMB reaction system and thus caused changes in color and absorbance, which facilitated a colorimetric sensor for sulfite. After optimizing detection conditions, a facile and robust approach was developed for SO32- detection in food.

Holey cobalt oxyhydroxide nanosheets for the oxygen evolution reaction

Holey CoOOH nanosheets (CoOOH HNSs) are easily synthesized by a successive coordination–oxidation–hydrolysis strategy.

A rapid colorimetric method for determining glutathione based on the reaction between cobalt oxyhydroxide nanosheets and 3,3′,5,5′-Tetramethylbenzidine

As an antioxidant, glutathione (GSH) can react with reactive oxygen species (ROS) and heavy metals to help alleviate oxidative stress (OS) and damage in cells. Accurately measuring the GSH level is important to gauge the integrity of cell redox buffering capacity. In this work, a convenient method for qualitative and quantitative determination of GSH was developed based on the reaction between CoOOH nanosheets and 3,3′,5,5′-tetramethylbenzidine (TMB). Colorless TMB solution can be oxidized by CoOOH to oxidized TMB (oxTMB) which is blue in color. However, in the presence of GSH, CoOOH preferentially reacted with GSH, producing less oxTMB and lighting the blue color. The changes of the blue color of oxTMB can be directly observed by naked eyes and accurately measured by UV–vis absorbance at 652 nm. Based on that, GSH can be detected in a wide range from 0.1 to 300 µM with a low limit of detection of 0.08 μM which was performed with a quantitativehigh-throughput96-wellplate. In addition, GSH in human SH-SY5Y neuroblastoma cells was successfully determined using our method, and the results show excellent agreement with those measured by a commercial GSH detection kit based on the use of Ellman’s reagent.

A fluorometric aptasensor for methamphetamine based on fluorescence resonance energy transfer using cobalt oxyhydroxide nanosheets and carbon dots.

Cobalt oxyhydroxide (CoOOH) nanosheets are efficient fluorescence quenchers due to their specificoptical properties and high surface area. The combination of CoOOH nanosheets and carbon dots (CDs) has not been used in any aptasensor based on fluorescence quenching so far. An aptamer based fluorometric assay is introduced that is making use of fluorescent CDs conjugated to the aptamer against methamphetamine (MTA), and of CoOOH nanosheets which reduce the fluorescence of the CDs as a quencher. The results revealed that the conjugated CDs with aptamers were able to enclose the CoOOH nanosheets. Consequently, fluorescence is quenched. If the aptamer on the CDbinds MTA, the CDs are detached from CoOOH nanosheets. As a result, fluorescence is restored proportionally to zheMTA concentration. The fluorometriclimit of detection is 1nM with a dynamic range from 5 to 156nM. The method was validated by comparing the results obtained by the new method to those obtained by ion mobility spectroscopy. Theoretical studies showed that the distance between CoOOH nanosheet and C-Ds is approximately 7.6Å which can illustrate the possibility of FRET phenomenon. The interactions of MTA and the aptamer were investigated using molecular dynamic simulation (MDS). Graphical abstract Carbon dots (C-Ds) were prepared from grape leaves, conjugated to aptamer, and adsorbed on CoOOH nanosheets. So, the fluorescence ofC-Ds is quenched. On addition of MTA, fluorescence is restored.

Ultrasensitive determination of ascorbic acid by using cobalt oxyhydroxide nanosheets to enhance the chemiluminescence of the luminol-H2O2 system.

Ascorbic acid (AA) as an essential vitamin in the human body participates in various physiological reactions and plays a key role in many biochemical processes. Therefore, it is of vital importance to monitor and quantify AA in commercial tablets, beverages and food. In this work, a rapid and ultrasensitive chemiluminescence (CL) system for the detection of AA was developed, in which ultrathin cobalt oxyhydroxide (CoOOH) nanosheets were applied in the conventional luminol–H2O2 CL system. The results showed that ultrathin CoOOH nanosheets as a catalyzer remarkably improved the CL intensity of the CoOOH–luminol–H2O2 system, up to about 1400-fold. Under the optimized conditions, the CL inhibition efficiencies increase linearly with the concentrations of AA in the range of 1–500 pmol L−1, and the limit of detection was 39 fmol L−1. Moreover, the proposed CL system was successfully applied in the determination of AA in medicinal tablets with satisfactory results.

Fluorometric determination of ascorbic acid by exploiting its deactivating effect on the oxidase–mimetic properties of cobalt oxyhydroxide nanosheets

Nanosheets of cobalt oxyhydroxide (CoOOH) are found to exhibit oxidase–like activity and can catalyze the oxidation of the substrate 3,3′,5,5′–tetramethylbenzidine (TMB) by oxygen in weakly acidic solution even in the absence of hydrogen peroxide. On the basis of this property, a fluorometric assay was designed in which the blue oxidation product of TMB (oxTMB) reduces the intensity of the fluorescence of albumin–stabilized gold nanoclusters (BSA–AuNCs). The fluorescence of the AuNCs under 502 nm photoexcitation has a peak at 620 nm which overlaps the absorption band of oxTMB. As a result, fluorescence is reduced. The findings were used to develop a method for the fluorometric quantitation of ascorbic acid. Ascorbic acid is capable of destroying some of the CoOOH nanosheets, and hence catalytic oxidation is retarded and fluorescence will be less strongly reduced (i.e., reabsorbed). Fluorescence intensity increases in the 0.75 to 20 μM ascorbic acid concentration range, and the detection limit is 0.2 μM. The method is well reproducible (the relative standard deviation of 1.6% for 11 replicates at a 10 μM ascorbic acid level). The practicability of the method was demonstrated by the analysis of ascorbic acid in tablets and juices.

An aptasensor based on cobalt oxyhydroxide nanosheets for the detection of thrombin

An aptasensor based on a fluorophore-labelled aptamer and cobalt oxyhydroxide (CoOOH) nanosheets was developed for determining the concentration of thrombin.