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Rapid, accurate, reliable, and risk-free tracking of pathogenic microorganisms at the single-cell level is critical to achieve efficient source control and prevent outbreaks of microbial infectious diseases. For the first time, we report a promising approach for integrating the concepts of a remarkably large Stokes shift and dual-recognition into a single matrix to develop a pathogenic microorganism stimuli-responsive ratiometric fluorescent nanoprobe with speed, cost efficiency, stability, ultrahigh specificity, and sensitivity. As a proof-of-concept, we selected the Gram-positive bacterium Staphylococcus aureus (S. aureus) as the target analyte model, which easily bound to its recognition aptamer and the broad-spectrum glycopeptide antibiotic vancomycin (Van). To improve the specificity and short sample-to-answer time, we employed classic noncovalent π-π stacking interactions as a driving force to trigger the binding of Van and aptamer dual-functionalized near-infrared (NIR) fluorescent Apt-Van-QDs to the surface of an unreported blue fluorescent π-rich electronic carbon nanoparticles (CNPs), achieving S. aureus stimuli-responsive ratiometric nanoprobe Apt-Van-QDs@CNPs. In the assembly of Apt-Van-QDs@CNPs, the blue CNPs (energy donor) and NIR Apt-Van-QDs (energy acceptor) became close to allow the fluorescence resonance energy transfer (FRET) process, leading to a remarkable blue fluorescence quenching for the CNPs at ∼465 nm and a clear NIR fluorescence enhancement for Apt-Van-QDs at ∼725 nm. In the presence of S. aureus, the FRET process from CNPs to Apt-Van-QDs was disrupted, causing the nanoprobe Apt-Van-QDs@CNPs to display a ratiometric fluorescent response to S. aureus, which exhibited a large Stokes shift of ∼260 nm and rapid sample-to-answer detection time (∼30.0 min). As expected, the nanoprobe Apt-Van-QDs@CNPs showed an ultrahigh specificity for ratiometric fluorescence detection of S. aureus with a good detection limit of 1.0 CFU/mL, allowing the assay at single-cell level. Moreover, we also carried out the precise analysis of S. aureus in actual samples with acceptable results. We believe that this work offers new insight into the rational design of efficient ratiometric nanoprobes for rapid on-site accurate screening of pathogenic microorganisms at the single-cell level in the early stages, especially during the worldwide spread of COVID-19 today.

The noninvasive and specific detection of cancer cells in living subjects has been essential for the success of cancer diagnoses and treatments. Herein, we report a strategy of combining an αvβ3-integrin-receptor-targetable ligand, c-RGD, with the γ-glutamyl transpeptidase (GGT)-recognizable substrate, γ-glutamate (γ-Glu), to develop a tumor-targeting and GGT-activatable near-infrared (NIR)-fluorescent probe for the noninvasive imaging of tumors in living mice. We demonstrated that the probe’s fluorescence was off initially, but when the γ-Glu in the probe was specifically cleaved by GGT, the fluorescent product was released and could be selectively taken up by U87MG-tumor cells via αvβ3-receptor-mediated endocytosis. Remarkably, enhanced intracellular NIR fluorescence distributed mainly in the lysosomes was observed in the tumor cells only, showing that the probe was capable of differentiating the tumor cells from the GGT-positive, αvβ3-deficient normal cells. Moreover, the probe also showed a high selec...

Targeted delivery of intracellular stimuli-activatable photosensitizers (PSs) into tumor cells to achieve selective imaging and on-demand photodynamic therapy (PDT) of tumors has provided a vital opportunity for precise cancer diagnosis and therapy. In this paper, we report a tumor targeting and adenosine triphosphate (ATP)-activatable nanophotosensitizer Apt-HyNP/BHQ2 by modifying hybrid micellar nanoparticles with both nucleolin-targeting aptamer AS1411 and quencher BHQ2-labeled ATP-binding aptamer BHQ2-ATP-apt. We demonstrated that both of the fluorescence emissions at 555 and 627 nm were quenched by BHQ2 in Apt-HyNP/BHQ2, resulting in low PDT capacity. After selective entry into tumor cells through nucleolin-mediated endocytosis, the high concentration of intracellular ATP could bind to BHQ2-ATP-apt and trigger Apt-HyNP/BHQ2 dissociation, leading to turning “on” both fluorescence and PDT. The “off–on” fluorescence emissions at both 555 and 627 nm were successfully applied for dual color fluorescence i...