Facile and sensitive S1 endonuclease activity and inhibition assay using positively-charged Ag nanorods

A turn-on fluorescent probe via substitution-rearrangement for highly sensitive and discriminative detection of cysteine and its imaging in living cells

Biothiols play an important role in many physiological and pathological processes, especially in the occurrence of oxidative stress caused by abnormal cysteine (Cys) concentration. Therefore, it is particularly critical to develop a method that can specifically identify Cys to avoid interference from other biological analytes. However, most Cys-specific fluorescent probes are difficult to distinguish between homocysteine (Hcy) and glutathione (GSH). In this work, to avoid the interference of Hcy and GSH, we developed a fluorescent probe triarylimidazole-naphthalimide-piperazine-sulfonyl benzoxadiazole (TNP-SBD-Cl) based on fluorescence resonance energy transfer (FRET) on platform of naphthalimide-sulfonyl benzoxadiazole (SBD), the main SBD 4-chlorine groups have mild reactivity to undergo substitution and rearrangement to distinguish Hcy and GSH. The TNP-SBD-Cl response to Cys would turn on FRET and generate a new yellow fluorescence with a large Stokes shift (157 nm), and with excellent selectivity and low detection limit (0.87 μM). Moreover, TNP-SBD-Cl can be used to monitor Cys in living HeLa cells with low cytotoxicity, suggesting that it has markedly diagnostic significance in physiological and pathological processes.

Chemiluminescence "signal-on-off" dual signals ratio biosensor based on single-stranded DNA functions as guy wires to detect EcoR V

Signal output mode is the important part of biosensor. In general, "signal on" and "signal off" are two common output modes. The development of dual signals-based ratio analysis as a powerful diagnostic tool has attracted widespread attention in the biosensor field in recent years. Dual signals ratio sensors with "signal on" and "signal off" are more favored because of their low background signal and better sensitivity and selectivity. In this study, inspired by the idea that EcoR V can cut specific sites of DNA to produce two corresponding fragments, and by using the capturing probe as guy wires, a reliable and sensitive method for EcoR V assay is developed based on the ratio of dual chemiluminescence (CL) signals for the first time. In particular, in the existence of the objective EcoR V, the substrate DNA would be degraded into two double stranded oligonucleotides with blunt ends which include the sequence I and the sequence II, then they can separately compete with two different corresponding capture probes on magnetic beads (MBs). One of capture probe hybridized with the sequence I containing more guanine (G) bases that reacted with the phenylglyoxal (PG) to produce chemical reaction which triggered a positive CL signal output I ⁺ _CL as "signal-on"; another capture probe is priority to hybridize the sequence II, which triggered the weaker reporter DNA linked with horseradish peroxidase (HRP) probe to fall off the MBs, thereby outputting a negative CL signal I^-_CL as "signal-off". By comparing the linear relation and the correlation coefficient, the I^-_CL/I ⁺ _CL ratio method has better linear relation (0.01-10 U/mL) and higher sensitivity (0.0045 U/mL). In addition, this developed strategy of high selectivity which can directly detect low concentration of target EcoR V in human serum, and thus this dual ratio biosensor might offer a promising detection approach for clinical diagnostics.

A review on optical sensors based on layered double hydroxides nanoplatforms

In recent years, significant efforts have been devoted towards the fabrication and application of layered double hydroxides (LDHs) due to their tremendous features such as excellent biocompatibility with negligible toxicity, large surface area, high conductivity, excellent solubility, and ion exchange properties. Most impressive, LDHs offer a favorable environment to attach several substances such as quantum dots, fluorescein dyes, proteins, and enzymes, which leads to strengthening the catalytic properties or increasing the sensing selectivity and sensitivity of the resulted hybrids. With the extensive ongoing research on the application of nanomaterials, many studies have led to remarkable achievements in exploring LDHs as sensing nanoplatforms. In optical sensors, for instance, many sensing strategies were tailored based on the enzyme-mimicking properties of LDHs, including colorimetric and chemiluminescence procedures. Meanwhile, others were designed based on intercalating some fluorogenic substrates on the LDHs, whereby the sensing signal can be acquired by quenching or enhancing their fluorescence after the addition of analytes. In this review, we aim to summarize the recent advances in optical sensors that use layered double hydroxides as sensing platforms for the determination of various analytes. By outlining some representative examples, we accentuate the change of spectral absorbance, chemiluminescence, and photoluminescence phenomena triggered by the interaction of LDH or functionalized-LDH with the indicators and analytes in the system. And finally, current limitations and possible future orientation in designing further LDHs-based optical sensors are presented. It is hoped that this review will be helpful in assisting the establishment of more improved sensors based on LDHs features. Optical sensors based on layered double hydroxides (LDHs) nanoplatforms were reviewed. The sensing system and detection approaches were rationally reviewed. Possible future orientations were highlighted.

Shell-Isolated Nanoparticle-Enhanced Luminescence of Metallic Nanoclusters

Metallic nanoclusters (NCs) have molecular-like structures and unique physical and chemical properties, making them an interesting new class of luminescent nanomaterials with various applications in chemical sensing, bioimaging, optoelectronics, light-emitting diodes (LEDs), etc. However, weak photoluminescence (PL) limits the practical applications of NCs. Herein, an effective and facile strategy of enhancing the PL of NCs was developed using Ag shell-isolated nanoparticle (Ag SHIN)-enhanced luminescence platforms with tuned SHINs shell thicknesses. 3D-FDTD theoretical calculations along with femtosecond transient absorption and fluorescence decay measurements were performed to elucidate the enhancement mechanisms. Maximum enhancements of up to 231-fold for the [Au₇Ag₈(C≡C^tBu)₁₂]⁺ cluster and 126-fold for DNA-templated Ag NCs (DNA-Ag NCs) were achieved. We evidenced a novel and versatile method of achieving large PL enhancements with NCs with potential for practical biosensing applications for identifying target DNA in ultrasensitive surface analysis.