Cu(II)-Regulated On-Site Assembly of Highly Chemiluminescent Multifunctionalized Carbon Nanotubes for Inorganic Pyrophosphatase Activity Determination

Ultrasensitive PD-L1-Expressing Exosome Immunosensors Based on a Chemiluminescent Nickel-Cobalt Hydroxide Nanoflower for Diagnosis and Classification of Lung Adenocarcinoma

Programmed death ligand-1 (PD-L1)-expressing exosomes are considered a potential marker for diagnosis and classification of lung adenocarcinoma (LUAD). There is an urgent need to develop highly sensitive and accurate chemiluminescence (CL) immunosensors for the detection of PD-L1-expressing exosomes. Herein, N-(4-aminobutyl)-N-ethylisopropanol-functionalized nickel-cobalt hydroxide (NiCo-DH-AA) with a hollow nanoflower structure as a highly efficient CL nanoprobe was synthesized using gold nanoparticles as a "bridge". The resulting NiCo-DH-AA exhibited a strong and stable CL emission, which was ascribed to the exceptional catalytic capability and large specific surface area of NiCo-DH, along with the capacity of AuNPs to facilitate free radical generation. On this basis, an ultrasensitive sandwich CL immunosensor for the detection of PD-L1-expressing exosomes was constructed by using PD-L1 antibody-modified NiCo-DH-AA as an effective signal probe and rabbit anti-CD63 protein polyclonal antibody-modified carboxylated magnetic bead as a capture platform. The immunosensor demonstrated outstanding analytical performance with a wide detection range of 4.75 × 103-4.75 × 108 particles/mL and a low detection limit of 7.76 × 102 particles/mL, which was over 2 orders of magnitude lower than the reported CL method for detecting PD-L1-expressing exosomes. Importantly, it was able to differentiate well not only between healthy persons and LUAD patients (100% specificity and 87.5% sensitivity) but also between patients with minimally invasive adenocarcinoma and invasive adenocarcinoma (92.3% specificity and 52.6% sensitivity). Therefore, this study not only presents an ultrasensitive and accurate diagnostic method for LUAD but also offers a novel, simple, and noninvasive approach for the classification of LUAD.

Ultrasensitive NIR fluorometric assay for inorganic pyrophosphatase detection via Cu2+-PPi interaction using bimetallic Au-Ag nanoclusters

BACKGROUND

Inorganic pyrophosphatase (PPase) is key enzyme playing a key role in biochemical transformations such as biosynthesis of DNA and RNA, bone formation, metabolic pathways associated with lipid, carbohydrate and phosphorous. It has been reported that lung adenocarcinomas, colorectal cancer, and hyperthyroidism disorders can result from abnormal level of PPase. Therefore, it is of notable significance to develop simple and effective real time assay for PPase enzyme activity monitoring for screening of many metabolic pathways as well as for early disease diagnosis.

RESULT

The fluorometric detection of PPase enzyme in near infrared region-1 (NIR-1) has been carried out using bimetallic nanoclusters (LA@AuAg NCs). The developed sensing strategy was based on quenching of fluorescence intensity of LA@AuAg NCs upon interaction with copper (Cu2+) ions. The off state of LA@AuAg_Cu2+ ensemble was turned on upon addition of pyrophosphate anion (PPi) due to strong binding interaction between PPi and Cu2+. The catalytic conversion of PPi into phosphate anion (Pi) in the presence of PPase led to liberation of Cu2+ ions, and again quenched off state was retrieved due to interaction of free Cu2+ with LA@AuAg NCs. The ultrasensitive detection of PPase was observed in the linear range of 0.06-250 mU/mL with LOD as 0.0025 mU/mL. The designed scheme showed good selectivity towards PPase enzyme in comparison to other bio-substrates, along with good percentage recovery for PPase detection in real human serum samples.

SIGNIFICANCE

The developed NIR based assay is ultrasensitive, highly selective and robust for PPase enzyme and can be safely employed for other enzymes detection. This highly sensitive nature of biosensor was result of involvement of fluorescence-based technique and synergistic effect of dual metal in NIR based bimetallic NCs. Moreover, owing to the emission in NIR domain, in future, these nanoclusters can be safely employed for many biomedical applications for In vivo studies.

Simple, sensitive, colorimetric detection of pyrophosphate via the analyte-triggered decomposition of metal-organic frameworks regulating their adaptive multi-color Tyndall effect

This paper describes initially the application of the Tyndall effect (TE) of metal-organic framework (MOF) materials as a colorimetric signaling strategy for the sensitive detection of pyrophosphate ion (PPi). The used MOF NH2-MIL-101(Fe) was prepared with Fe3+ ions and fluorescent ligands of 2-amino terephthalic acid (NH2-BDC). The fluorescence of NH2-BDC in MOF is quenched due to the ligand-to-metal charge transfer effect, while the NH2-MIL-101(Fe) suspension shows a strong TE. In the presence of PPi analyte, the MOFs will undergo decomposition because of the competitive binding of Fe3+ by PPi over NH2-BDC, resulting in a significant decrease in the TE signal and fluorescence restoration from the released ligands. The results demonstrate that the new method only requires a laser pointer pen (for TE creation) and a smartphone (for portable quantitative readout) to detect PPi in a linear concentration range of 1.25-800 μM, with a detection limit of ~210 nM (3σ) which is ~38 times lower than that obtained from traditional fluorescence with a spectrophotometer (linear concentration range, 50-800 µM; detection limit, 8.15 µM). Moreover, the acceptable recovery of PPi in several real samples (i.e., pond water, black tea, and human serum and urine) ranges from 97.66 to 119.15%.

Smart fluorescent polysaccharides: Recent developments and applications

Polysaccharides are ubiquitous, generally benign in nature, and compatible with many tissues in biomedical situations, making them appealing candidates for new materials such as therapeutic agents and sensors. Fluorescent labeling can create the ability to sensitively monitor distribution and transport of polysaccharide-based materials, which can for example further illuminate drug-delivery mechanisms and therefore improve design of delivery systems. Herein, we review fluorophore selection and ways of appending polysaccharides, utility of the product fluorescent polysaccharides as new smart materials, and their stimulus-responsive nature, with focus on their biomedical applications as environment-sensitive biosensors, imaging, and as molecular rulers. Further, we discuss the advantages and disadvantages of these methods, and future prospects for creation and use of these self-reporting materials.

Cobalt Species-Loaded MOFs as Chemiluminescent Catalysts for Monitoring Carbendazim

The application of active metal-based nanoscale catalysts as signal enhancers for chemiluminescent immunoassay (CLIA) is restricted by poor thermodynamic stability and ease of aggregation. For the present exploration, zirconium-based MOFs UiO-66-NH2 were adopted as supports to load cobalt species by an impregnation-reduction approach. Cobalt species were uniformly distributed in the framework architecture of the MOF materials. The prepared cobalt-loaded MOF hybrids, noted as UiO-66-NH2/Co, display superior chemiluminescence (CL) catalytic activity owing to the introduction of cobalt catalytic centers. The CL catalytic capability of UiO-66-NH2/Co hybrids is about 18 times of that of free cobalt ions at the same cobalt amount. The results of mechanism exploration manifest that the hybrids are capable of accelerating the decay of hydrogen peroxide and promoting the yield of reactive oxygen species. Based on their remarkable CL catalytic capability, a CLIA approach was proposed to monitor carbendazim by adopting the hybrids as signal probes, which showed the merits of high sensitivity and satisfactory selectivity. Carbendazim was quantitated within a concentration range of 0.05 to 60 ng mL-1, with a detection limit of 19.8 pg mL-1. The results for monitoring spiked samples verify the acceptable practicality of the proposed CLIA approach.

Determination of acetic acid in enzymes based on the cataluminescence activity of graphene oxide-supported carbon nanotubes coated with NiMn layered double hydroxides

A cataluminescence (CTL) method has been developed for the rapid determination of acetic acid in enzyme products. The NiMn LDH/CNT/GO was synthesized based on the nanohybridization of NiMn layered double hydroxide (NiMn LDH), carbon nanotubes (CNTs), and graphene oxide (GO). The composite has excellent CTL activity against acetic acid. It could be ascribed to the larger specific surface area and more exposure to active sites. NiMn LDH/CNT/GO is used as a catalyst in the CTL method based on its special structure and advantages. There is a linear relationship between CTL response and the acetic acid concentration in the range 0.31-12.00 mg·L^-1 with the detection limit of 0.10 mg·L^-1. The developed method is rapid and takes only about 13 s. The method is applied to the determination of acetic acid in enzyme samples with little sample preparation. The result of the CTL method shows good agreement with that of the gas chromatography method. The proposed CTL method possesses promising potential in the quality monitoring of enzymes.

A copper ion-mediated on-off-on gold nanocluster for pyrophosphate sensing and bioimaging in cells

Herein, gold nanoclusters (AuNCs@EW@Lzm, AuEL) with the bright red fluorescence at 650 nm were prepared by egg white and lysozyme as double protein ligands, which exhibited good stability and high biocompatibility. The probe displayed highly selective detected pyrophosphate (PPi) based on Cu²⁺-mediated AuEL fluorescence quenching. Specifically, the fluorescence of AuEL was quenched once the Cu²⁺/Fe³⁺/Hg²⁺ is added to chelate with amino acids on the AuEL surface, respectively. Interestingly, the fluorescence of quenched AuEL-Cu²⁺ was significantly recovered by PPi, but not the other two. This phenomenon was attributed to the stronger bond between PPi and Cu²⁺ than that of Cu²⁺ with AuEL nanoclusters. The results demonstrated a good linear relationship between PPi concentration and the relative fluorescence intensity of AuEL-Cu²⁺ in the range of 131.00-685.40 μM with a detection limit of 2.56 μM. In addition, the quench AuEL-Cu²⁺ system can also be recovered in acidic environments (pH ≤ 5). And the as-synthesized AuEL showed excellent cell imaging and target the nucleus. Thus the fabrication of AuEL offers a facile strategy for efficient PPi assay and offers the potential for drug/gene delivery to the nucleus.

Washing-Free and Label-Free Onsite Assay for Inorganic Pyrophosphatase Activity Using a Personal Glucose Meter

In this study, we demonstrated a personal glucose meter-based method for washing-free and label-free inorganic pyrophosphatase (PPase) detection, which relies on the cascade enzymatic reaction (CER) promoted by hexokinase and pyruvate kinase. In principle, the absence of target PPase enables adenosine triphosphate sulfurylase to catalyze the conversion of pyrophosphate (PPi) to ATP, a substrate of CER, which results in the significant reduction of glucose levels by the effective CER process. In contrast, the PPi cleavage activity works in the presence of target PPase by decomposing PPi to orthophosphate (Pi). Therefore, the CER process cannot be effectively executed, leading to the maintenance of the initial high glucose level that may be measured by a portable personal glucose meter. Based on this novel strategy, a quantitative evaluation of the PPase activity may be achieved in a dynamic linear range of 1.5-25 mU/mL with a detection limit of 1.18 mU/mL. Compared with the previous PPase detection methods, this method eliminates the demand for expensive and bulky analysis equipment as well as a complex washing step. More importantly, the diagnostic capability of this method was also successfully verified by reliably detecting PPase present in an undiluted human serum sample with an excellent recovery ratio of 100 ± 2%.

Copper (II) Ion-Modified Gold Nanoclusters as Peroxidase Mimetics for the Colorimetric Detection of Pyrophosphate

Copper (II) ions have been shown to greatly improve the chemical stability and peroxidase-like activity of gold nanoclusters (AuNCs). Since the affinity between Cu²⁺ and pyrophosphate (PPi) is higher than that between Cu²⁺ and AuNCs, the catalytic activity of AuNCs-Cu²⁺ decreases with the introduction of PPi. Based on this principle, a new colorimetric detection method of PPi with high sensitivity and selectivity was developed by using AuNCs-Cu²⁺ as a probe. Under optimized conditions, the detection limit of PPi was 0.49 nM with a linear range of 0.51 to 30,000 nM. The sensitivity of the method was three orders of magnitude higher than that of a fluorescence method using AuNCs-Cu²⁺ as the probe. Finally, the AuNCs-Cu²⁺ system was successfully applied to directly determine the concentration of PPi in human urine samples.

Novel cobalt-based metal-organic frameworks with superior catalytic performance on N-(4-aminobutyl)-N-ethylisoluminol chemiluminescent reaction

Novel cobalt-based metal-organic frameworks (Co MOFs) were synthesized by a facile "controlled synthesis" strategy. The MOFs displayed superior catalytic performance on the chemiluminescent (CL) reaction between N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and H₂O₂. UV-vis absorption, CL spectrum, ESR, and radical scavenger experiments were conducted for clarifying the catalytic mechanism of Co MOFs. All results revealed that Co MOFs can accelerate decomposition of H₂O₂ and production of OH^•, O₂^•-as well as ¹O₂ radicals. The rapid reaction between these reactive oxygen species and ABEI resulted in the generation of ABEI-ox∗. The excited-state oxidation product emitted a very intensive CL signal with a maximal emission wavelength of 430 nm as it returned to the ground state. To explore their application potential in CL assay, Co MOFs were used as powerful CL reaction catalyst for establishing a very sensitive method for immunoassay of aflatoxin B₁. The detection range was 0.05-60 ng mL^-1, and the limit of detection was 4.3 pg mL^-1. The result for detecting herbal medicine samples demonstrates the acceptable reliability of the Co MOFs-based CL immunoassay. The proof-of-principle work verifies the application potential of Co MOFs on boosting intensive CL signal, and meets the demand for high sensitivity in various bioassay fields.

Visual and dual-fluorescence homogeneous sensor for the detection of pyrophosphatase in clinical hyperthyroidism samples based on selective recognition of CdTe QDs and coordination polymerization of Ce3+

A visual / dual fluorescent strategy based on selective recognition of QDs and coordination polymerization of Ce³⁺ was developed for pyrophosphatase detection.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.