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.