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Graphene-related−TiO 2 (G−TiO 2 ) nanocomposites show enhanced photocatalytic performance, not only due to promoting photogenerated electrons migration but also by extending optical absorption to the visible light range. However, little is known about the origin of the visible light activity, which seems to depend much on the precursor of the titanium source. In this study, an efficient visible light active G− TiO 2 -413 was prepared by hydrothermally treating a graphene oxide (GO) suspension and TiO 2 sol with undergrown TiO 2 nanoparticles at 413 K. According to XRD, DRS, TEM, FTIR, Raman, and ESR analyses, when in situ growing TiO 2 nanoparticles from hydrolyzed titanium alkoxides in hydrothermal conditions, a strong chemical interaction appears at the interface of GO sheets and the underdeveloped loosely packed polymeric Ti−O−Ti skeletons, so as to facilitate retaining more alkoxyl groups, inducing crystal disorders, and creating oxygen vacancies. All of these contribute to the significantly enhanced visible light activity of G−TiO 2 -413. This sheds new light on the development of visible light responsive TiO 2 -based photocatalysts via surface modification approaches.

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The emergence of drug‐resistant bacteria is becoming the focus of global public health. Early‐stage pathogen bioimaging will offer a unique perspective to obtain infection information in patients. A photoacoustic (PA) contrast agent based on functional peptide modified gold nanoparticles (AuNPs@P1) is developed. These nanoparticles can be specifically tailored surface peptides by bacterial overexpressed enzyme inducing in situ aggregation of the gold nanoparticles. In the meantime, the close aggregation based on the hydrogen bonding, π–π stacking, and hydrophobic interaction of the peptide residues on the surface of gold nanoparticles exhibits a typical redshifted and broadened plasmon band. In addition, this active targeting and following in situ stimuli‐induced aggregation contribute to increased nanoparticle accumulation in the infected site. Finally, the dynamic aggregation of AuNPs@P1 results in dramatically enhanced photoacoustic signals for bioimaging bacterial infection in vivo with high sensitivity and specificity. It is envisioned that this PA contrast agent may provide a new approach for early detection of bacterial infection in vivo.