A series of carbon nanoparticles (CNPs) with emission wavelength ranging from 483 to 525 nm were prepared by hydrothermal treatment of poly-3-thiopheneacetic acid (PTA) and NaOH. The emission wavelength and surface oxidation degree of CNPs were shown to be controllable by simply adjusting NaOH concentration. These CNPs presented obvious fluorescence spectral response toward copper ions (Cu²⁺) through static quenching caused synergistically by electron transfer and inner filter effect. The O- and S-containing groups on the surface of CNPs were demonstrated to be responsible for their outstanding sensing performance. Based on that, a CNPs-based ratiometric fluorescent probe for Cu²⁺ with a high fluorescence quenching rate constant of 1.4 × 10⁵ L/mol and a short response time (10 s) was developed. Their practical applications in detecting Cu²⁺ in pond water and living cells were also demonstrated.

C dots (CDs) have shown great potential in bioimaging and phototherapy. However, it is challenging to manipulate their fluorescent properties and therapeutic efficacy to satisfy the requirements for clinic applications. In this study, we prepared S, Se-codoped CDs via a hydrothermal method and demonstrated that the doping resulted in excitation wavelength-independent near-infrared (NIR) emissions of the CDs, with peaks at 731 and 820 nm. Significantly, the CDs exhibited a photothermal conversion efficiency of ~58.2%, which is the highest reported value for C nanostructures and is comparable to that of Au nanostructures. Moreover, the CDs had a large two-photon absorption cross section (~30, 045 GM), which allowed NIR emissions and the photothermal conversion of the CDs through the two-photon excitation (TPE) mechanism. In vitro and in vivo tests suggested that CDs can function as new multifunctional phototheranostic agents for the TPE fluorescence imaging and photothermal therapy of cancer cells.

Metal-free, organic-dye-based fluorescent nanorods were fabricated through a simple solvent-exchange procedure. The as-prepared nanorods exhibit low toxicity to living cells and excellent photostability. Furthermore, they are stable in solutions of various pHs and high ionic strength and in solutions with interfering metal ions. Compared with the free DPP-Br molecules in THF, these nanorods exhibit larger Stokes shift, broader absorption spectra, and greatly improved photostability. We successfully demonstrated the application of the nanorods, including their aforementioned beneficial characteristics, as a good fluorescence probe for bio-imaging.

We report a facile assay for the rapid visual detection of lipopolysaccharide (LPS) molecules down to the low nanomolar level by taking advantage of the electrostatic interaction between LPS molecules and cysteamine-modified gold nanoparticles (CSH–Au NPs). The large amount of negatively charged groups on the LPS molecules make LPS highly negatively charged. Thus, when modified with cysteamine, the positively charged gold nanoparticles can aggregate in the presence of trace amounts of LPS. The probe is simple, does not require any advanced instrumentation, and the limit of detection (LOD) was determined to be as low as 3.3 × 10⁻¹⁰ mol/L. To the best of our knowledge, it is the most sensitive synthetic LPS sensor reported so far.