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Sensitive platform: The use of graphene oxide (GO) as a platform for the sensitive and selective detection of DNA and proteins is presented. The interaction of GO and dye-labeled single-stranded DNA leads to quenching of the dye fluorescence. Conversely, the presence of a target DNA or protein leads to the binding of the dye-labeled DNA and target, releasing the DNA from GO, thereby restoring the dye fluorescence (see picture).

A novel sensing system has been designed for Cu(2+) ion detection based on the quenched fluorescence (FL) signal of branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu(2+) ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs' FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu(2+) with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu(2+) ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system.

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A facile method has been developed to extract oxidized carbon quantum dots (QDs) directly from activated carbon (AC) by chemical oxidation. The method has several advantages including low cost, high yield of QDs (>10%), and large-scale production. The as-prepared oxidized carbon QDs are mainly graphitic structure nanocrystals of 3-4 nm in diameter, have abundant carboxyl groups at their surfaces, and exhibit strong electrochemiluminescent (ECL) activity, suggesting promising applications in ECL biosensing and imaging. The ECL properities, including ECL activities in the absence and presence of coreactants, effects of the size and surface passivation on the oxidized carbon QDs ECL were investigated and discussed in detail.