Gold nanoparticles functionalized with Ru(II)bipyridyl labeled DNA as a luminescent probe for the sensitive determination of DNase I

Enzyme activity termination by titanium carbide nanosheet and its application for the detection of deoxyribonuclease I

Deoxyribonuclease I (DNase I) is a typical nuclease that plays key roles in many physiological processes and the development of a novel biosensing strategy for DNase I detection is of fundamental significance. In this study, a fluorescence biosensing nanoplatform based on a two-dimensional (2D) titanium carbide (Ti₃C₂) nanosheet for sensitive and specific detection of DNase I was reported. Fluorophore-labeled single-stranded DNA (ssDNA) can be spontaneously and selectively adsorbed on Ti₃C₂ nanosheet through the hydrogen bond and metal chelate interaction between phosphate groups of ssDNA and titanium of Ti₃C₂ nanosheet, resulting in effective quenching of the fluorescence emitted by fluorophore. Notably, it was found the enzyme activity of DNase I will be terminated by the Ti₃C₂ nanosheet. Therefore, the fluorophore-labeled ssDNA was firstly digested by DNase I and the "post-mixing" strategy of Ti₃C₂ nanosheet was chosen to evaluate the enzyme activity of DNase I, which provided the possibility of improving the accuracy of the biosensing method. Experimental results demonstrated that this method can be utilized for quantitative analysis of DNase I activity and exhibited a low detection limit of 0.16 U/ml. Additionally, the evaluation of DNase I activity in human serum samples and the screening of inhibitors with this developed biosensing strategy were successfully realized, implying that it has high potential as a promising nanoplatform for nuclease analysis in bioanalytical and biomedical fields.

"Plug and Play" logic gate construction based on chemically triggered fluorescence switching of gold nanoparticles conjugated with Cy3-tagged aptamer

Gold nanoparticles (AuNPs) conjugated with Cy3-tagged aptamer which can specifically recognize chloramphenicol (CAP) (referred to as AuNPs-AptCAP) are described. CAP can trigger the configuration change of CAP binding aptamer, and thus switching the fluorescence of AuNPs-AptCAP through changing the efficiency of the fluorescence resonance energy transfer (FRET) system with Cy3 as donors and AuNPs as recipients. AuNPs-AptCAP exhibits a linear range of CAP concentrations from 26.0 to 277 μg L^-1 with a limit of detection of 8.1 μg L^-1 when Cy3 was excited at 530 nm and emission was measured at 570 nm. More importantly, AuNPs-AptCAP can be utilized as signal transducers for the build-up of a series of logic gates including YES, PASS 0, INH, NOT, PASS 1, and NAND. Utilizing the principle of a metal ion-mediated fluorescence switch together with a strong metal ion chelator, the fluorescence of AuNPs-AptCAP could be modulated by adding metal ions and EDTA sequentially. Therefore, a "Plug and Play" logic system based on AuNPs-AptCAP has been realized by simply adding other components to create new logic functions. This work highlights the advantages of simple synthesis and facile fluorescence switching properties, which will provide useful knowledge for the establishment of molecular logic systems. Graphical abstract.

Transition metal complex/gold nanoparticle hybrid materials

Gold nanoparticles (AuNPs) are of considerable interest for diverse applications in areas such as medicine, catalysis, and sensing. AuNPs are generally surface-stabilized by organic matrices and coatings, and while the resultant organic compound (OC)/AuNP hybrids have been explored extensively, they are not suitable for certain applications (e.g. those necessitating reversible redox behaviour and/or long excited-state lifetimes), and they often suffer from low photo- and/or thermal stability. Transition metal complex (TMC)/AuNP hybrids have recently come to the fore as they circumvent some of the aforementioned shortcomings with OC/AuNP hybrids. This review summarizes progress thus far in the nascent field of TMC/AuNP hybrids. The structure and composition of extant TMC/AuNP hybrids are briefly reviewed and the range of TMCs employed in the shell of the hybrids are summarized, the one-phase, two-phase, and post-nanoparticle-synthesis synthetic methods to TMC/AuNP hybrids are discussed and contrasted, highlighting the advantages of variants of the last-mentioned procedure, and the utility of the various characterization techniques is discussed, emphasizing the need to employ multiple techniques in concert. Applications of TMC/AuNP hybrids in luminescence, electrochemical, and electro-optical sensing are described and critiqued, and their uses and potential in imaging, photo-dynamic therapy, nonlinear optics, and catalysis are assessed.

Coupling coumarin to gold nanoparticles by DNA chains for sensitive detection of DNase I

A kind of coumarin-modified gold nanoparticle by the bridge of dsDNA chains was designed and synthesized for sensitive detection of DNase I. The fluorescence of coumarin 343 at emission wavelengths of 491 nm excited at 440 nm was quenched by the gold nanoparticles due to the energy transfer process after the coumarin 343 was connected on the gold nanoparticles by DNA chains. When dsDNA chains were cut off by DNase I, the coumarin 343 molecules were released from gold nanoparticles and the fluorescence of coumarin 343 would be restored. The DNase I activity could be detected by this fluorescence assay with a high sensitivity based on the change of the energy transfer efficiency. The intensity of restored fluorescence is linearly related to the quantity of DNase I in the range from 1.0 to 40 mU/mL with a detection limit of 0.22 mU/mL. This design idea could render a useful way to develop similar molecular or enzyme sensor in analytical or biological fields.

An aptamer-based colorimetric lead(II) assay based on the use of gold nanoparticles modified with dsDNA and exonuclease I

The authors describe a colorimetric method for the sensitive and selective detection of Pb(II). It is based on the use exonuclease I (Exo I), a Pb(II)-binding aptamer bound to gold nanoparticles (AuNPs), and a DNA strand that complementary to the aptamer. In the absence of Pb(II), the dsDNA on the AuNPs prevents aggregation of the AuNPs in the presence of NaCl. In the presence of Pb(II), however, the aptamer binds Pb(II) and complementary strand is released and digested by Exo I. As a result, the solution of AuNPs undergoes a color change from red to purple if salt is added to the sample. The assay is selective for Pb(II) and has a limit of detection as low as 2.4 nM. It was successfully applied to the determination of Pb(II) in spiked tap water. Graphical abstract Schematic presentation of the aptamer based method for Pb²⁺ detection via salt-induced aggregation of gold nanoparticles and colorimetric quantitation.