Hairpin stabilized fluorescent silver nanoclusters for quantitative detection of NAD+ and monitoring NAD+/NADH based enzymatic reactions

A novel "on-off" SERS nanoprobe based on sulfonated cellulose nanofiber-Ag composite for selective determination of NADH in human serum

A novel S-CNF-based nanocomposite was created using sulfonated cellulose nanofiber (S-CNF) to enable the detection of NADH in serum by surface-enhanced Raman spectroscopy (SERS). The numerous hydroxyl and sulfonic acid groups on the S-CNF surface absorbed silver ions and converted them to silver seeds, which formed the load fulcrum. After adding a reducing agent, silver nanoparticles (Ag NPs) were firmly adhered to the S-CNF surface to form stable 1D "hot spots." The S-CNF-Ag NP substrate demonstrated outstanding SERS performance, including good uniformity with an RSD of 6.88% and an enhancement factor (EF) of 1.23 × 107. Owing to the anionic charge repulsion effect, the S-CNF-Ag NP substrate still maintains remarkable dispersion stability after 12 months of preservation. Finally, S-CNF-Ag NPs' surface was modified with 4-mercaptophenol (4-MP), a special redox Raman signal molecule, to detect reduced nicotinamide adenine dinucleotide (NADH). The results showed that the detection limit (LOD) of NADH was 0.75 μM; a good linear relationship (R2 = 0.993) was established in the concentration range 10-6 - 10-2 M. The SERS nanoprobe enabled rapid detection of NADH in human serum without any complicated sample pretreatment and provides a new potential to detect biomarkers.

Current Status and Future Perspectives of Lactate Dehydrogenase Detection and Medical Implications: A Review

The demand for glucose uptake and the accompanying enhanced glycolytic energy metabolism is one of the most important features of cancer cells. Unlike the aerobic metabolic pathway in normal cells, the large amount of pyruvate produced by the dramatic increase of glycolysis in cancer cells needs to be converted to lactate in the cytoplasm, which cannot be done without a large amount of lactate dehydrogenase (LDH). This explains why elevated serum LDH concentrations are usually seen in cancer patient populations. LDH not only correlates with clinical prognostic survival indicators, but also guides subsequent drug therapy. Besides their role in cancers, LDH is also a biomarker for malaria and other diseases. Therefore, it is urgent to develop methods for sensitive and convenient LDH detection. Here, this review systematically summarizes the clinical impact of lactate dehydrogenase detection and principles for LDH detection. The advantages as well as limitations of different detection methods and the future trends for LDH detection were also discussed.

Non-Destructive Monitoring via Electrochemical NADH Detection in Murine Cells

Nicotinamide adenine dinucleotide (NADH) is an important cofactor involved in metabolic redox reactions in living cells. The detection of NADH in living animal cells is a challenge. We developed a one-step monitoring method for NADH via an electrocatalytic reaction that uses a surface-modified, screen-printed electrode (SPE) having a redox active monolayer 4'-mercapto-N-phenlyquinone diamine (NPQD) formed by a self-assembled monolayer (SAM) of an aromatic thiol, 4-aminothiophenol (4-ATP). This electrode has a limit of detection (LOD) of 0.49 μM and a sensitivity of 0.0076 ± 0.0006 μM/μA in cell culture media, which indicates that it retains its selectivity. The applicability of this NADH sensor was demonstrated for the first time by cell viability monitoring via NADH-sensing in cell culture supernatants.

Determination of NADH by Surface Enhanced Raman Scattering Using Au@MB@Ag NPs

Nicotinamide adenine dinucleotide (NADH) is an important coenzyme involved in various metabolic processes of living cells. As an important biomarker, NADH is associated with breast cancer and Alzheimer’s disease. In this paper, silver plated gold core–shell nanoparticles containing Raman signal molecules were synthesised on the basis of bare gold. Using the Raman peak corresponding to the 4-mercaptobenzonitrile (MB) silent region C≡N vibration for quantification, while avoiding competition with the precious metal surface binding site to be measured, it can also be free from the interference of endogenous biomolecules. On the one hand, it can correct the working curve, on the other hand, it can avoid competing with the binding site. Compared with the core–shell structure prepared here, the limit of detection (LOD) for NADH was only 10−5 M for bare gold and the LOD for the core–shell structure prepared on the basis of bare gold was 3.3 × 10−7 M. In terms of correction, with Rhodamine 6G (R6G) as a Raman signalling molecule, the R2 value before SERS detection and correction is only 0.9405, and the R2 value after correction increases to 0.9853. The unique fingerprint peak of SERS was used to realise the quantitative detection of NADH, which realizes the detection of NADH in complex biological samples of serum and provides the possibility for expanding the early diagnosis of breast cancer.

A trifunctional split dumbbell probe coupled with ligation-triggered isothermal rolling circle amplification for label-free and sensitive detection of nicotinamide adenine dinucleotide

The nicotinamide adenine dinucleotide (NAD⁺) is an important small biomolecule that participates in a variety of physiological functions, and it has been regarded as a potential biomarker for disease diagnosis and a promising target for disease treatment. The conventional methods for NAD⁺ assay often suffer from complicated procedures, expensive labeling, poor selectivity, and unsatisfactory sensitivity. Herein, we develop a label-free and sensitive method for NAD⁺ assay based on the integration of a trifunctional split dumbbell probe with ligation-triggered isothermal rolling circle amplification (RCA). We design a trifunctional split dumbbell probe that can act as a probe for NAD⁺ recognition, a template for RCA reaction, and a substrate for SYBR Green I binding. In the presence of target NAD⁺, it can serve as a cofactor to active E. coli DNA ligase which subsequently catalyzes the ligation of split dumbbell probe to form a circular template for RCA reaction, generating numerous dumbbell probe amplicons which can be easily and label-free monitored by using SYBR Green I as the fluorescent indicator. Due to the high fidelity of NAD⁺-dependent ligation and high amplification efficiency of RCA amplification, this method exhibits high sensitivity with a detection limit of 85.6 fM and good selectivity with the capability of discriminating target NAD⁺ from its analogs. Moreover, this method can be applied for accurate and sensitive detection of NAD⁺ in complex biological samples and cancer cells, holding great potential in NAD⁺-related biological researches and clinical diagnosis.

DNA-Hairpin-Templated Silver Nanoclusters: A Study on Stem Sequence

DNA hairpins are widely used to synthesize silver nanoclusters (AgNCs) with excellent optical properties due to their specific secondary structure. Hairpin-AgNCs have been popularly employed for sensoring applications, while no systematic study has been done about the effect of stem sequence on the fluorescence property of hairpin-AgNCs. In this presented work, the synthesizing conditions of hairpin-AgNCs were fully examined first. Then, the effect of percentage content and distribution of GC base pairs as well as stem length on the fluorescence property of hairpin-AgNCs were studied. Intriguing phenomena were observed and basic conclusions were drawn, which would be helpful to understand the hairpin-AgNCs comprehensively and instructional for the applications using hairpin-AgNC probes.

DNA metallization: principles, methods, structures, and applications

This review summarizes the research activities on DNA metallization since the concept was first proposed in 1998, covering the principles, methods, structures, and applications.

Metal-DNA Interactions Improve signal in High-Resolution Melting of DNA for Species Differentiation of Plasmodium Parasite

The success of high-resolution melting (HRM) analysis for distinguishing similar DNAs with minor base mismatch differences is limited. Here, metal-mediated structural change in DNA has been exploited to amplify HRM signals leading to differentiation of target DNAs in an orthologous gene corresponding to four Plasmodium species. Conserved 26-mer ssDNAs from ldh gene of the four Plasmodium species were employed as targets. A capture probe (CP) that is fully complementary to the Plasmodium falciparum target (FT) and has two base mismatches each, with the targets of Plasmodium vivax (VT), Plasmodium malariae, (MT), and Plasmodium ovale (OT), was considered. The DNA duplexes were treated with metal ions for structural perturbation and analyzed by HRM. Distinct resolution of melting fluorescence signal in otherwise identical HRM profiles for each of the DNA duplexes was achieved by using Ca⁺² or Mg⁺² ions, where, Ca⁺² conferred higher resolution. The increase in resolution for CP-FT versus CP-OT, CP-FT versus CP-VT, CP-FT versus CP-MT, CP-VT versus CP-OT, and CP-MT versus CP-OT with Ca-DNA as compared to control was 67.3-, 20.4-, 22.0-, 10.9-, and 8.3-fold, respectively. The signal resolution was the highest at pH 8. The method could detect 0.25 pmol/µl of the target DNA. Structural analysis showed that Ca⁺² and Mg⁺² ions perturbed the structure of DNA. This perturbation helped to improve HRM signal resolution among DNA targets corresponding to the orthologous gene of four Plasmodium species. This novel approach has potential application not only for Plasmodium species-specific diagnosis but also for differentiation of DNAs with minor sequence variation.