Fok I cleavage–inhibition strategy for the specific and accurate detection of transcription factors

Label-free triplex DNA-based biosensing of transcription factor using fluorescence resonance energy transfer between N-doped carbon dot and gold nanoparticle

Herein, a new turn-on fluorescent assay was established as a platform for the sensing of transcription factor NF-kB p50 based on triplex DNA labeled with N-doped carbon dots (NCDs) and gold nanoparticles (AuNPs) as donors and acceptors, respectively in the fluorescence resonance energy transfer (FRET) system. The synthetized nanoparticles were studied by different characterization techniques. A labeled DNA molecule was designed to form a triplex when no target protein existence and reported its formation by the change in FRET efficiency. While the triplex DNA was formed, the fluorescence of carbon dots at 503 nm (excitation at 460 nm) was quenched by FRET between NCD and AuNP. However, presence of NF-kB p50 followed by the considerable enhancement in the fluorescence intensity caused by the release of AuNPs labeled single stranded DNA from the triplex DNA structure, used for sensitive determination of the transcription factor. This technique showed a linearity (R2 = 0.9943) in the range of 20-150 pM with a limit of detection of 9 pM for the determination of NF-kB p50. Moreover, the sequence-specific triplex-based biosensor could discriminate NF-kB p50 from the other proteins with high selectively. Our results suggest that the biosensor provides a generalizable platform for rapid detection of NF-kB p50 in synthetic medium, promising in prevention and early diagnosis of cancer.

Ultrasensitive colorimetric detection of NF-κB protein at picomolar levels using target-induced passivation of nanoparticles

We developed a highly sensitive and selective sensor based on the nanoprobe conjugates of catalytic nanoparticles and double-stranded DNA (dsDNA) for the colorimetric detection of NF-κB protein. The sensing mechanism takes advantage of the catalytic activity of nanoparticle surfaces and the specific binding of NF-κB to a dsDNA sequence. In the presence of NF-κB, the highly selective interactions between dsDNA and NF-κB lead to the passivation of the catalytic nanoparticle surfaces, impeding the sodium borohydride-mediated reduction rate of 4-nitrophenol. The correlation between the NF-κB concentration and the visualized reduction rate of 4-nitrophenol from yellow to colorless clearly demonstrates the highly quantitative nature of the sensor. Importantly, this sensor can conclusively detect concentrations as low as 6.39 pM of NF-κB, which to best of our knowledge is the lowest limit of detection for a colorimetric NF-κB detection system. The excellent sensitivity of this sensor relies on the high binding constant of NF-κB to dsDNA and the catalytic activity of nanoparticle surfaces for the signal amplification. This sensor allows visual detection without the need for any spectrometric instrumentation. We also determined the various parameters such as the pH, temperature, incubation time, and salt concentration for optimal NF-κB-dsDNA interactions. Finally, we demonstrated the performance of the sensor with simulated sample analysis. Graphical abstract A highly sensitive and selective colorimetric detection of protein NF-κB using the nanoprobeconjugates of catalytic gold nanoparticles and double-stranded DNA (dsDNA) has been developed.