Proximity sequence-dependent spectral conversion of silver nanoclusters and construction of ratiometric nanoprobe

In this work, a novel ratiometric nanoprobe was developed based on the spectral conversion of silver nanoclusters. Through systematical investigating the effect of proximity sequence on silver nanoclusters, the proximity sequence with poly G or poly C tail is found to have the ability to induce the spectral conversion of silver nanoclusters (from yellow-emitting to red-emitting), while other proximity sequences cannot induce the phenomenon under the same condition. The spectral conversion efficiency of silver nanoclusters can be regulated by the length of proximity sequences. The conversion mechanism was further characterized and confirmed by fluorescence spectroscopy and transmission electron microscopy. By changing the hybridization sequence, the spectral conversion of silver nanoclusters by proximity sequence with poly G was universal. Besides, based on this phenomenon, a single fluorophore ratiometric probe for accurate detection of mercury ions was developed. Both in buffer and actual water samples, this ratiometric probes presented good sensitivity and selectivity for mercury ions detection. In comparison with conventional ratiometric probes, our method is unique not only because it requires only a single preparation step, but because it has high signal to noise ratio. A good detection capability exhibited with a detectable minimum target concentration of 0.01 μM, which was comparable to or even better than some reported fluorescence methods. This work not only has a certain guiding significance for scientifically design proximity sequence DNA sequences that can induce the spectrum conversion phenomenon of silver nanoclusters, but also reduces the marginal cost in the experiment.