Cui Liu

A highly sensitive detection method for ALP was established based on fluorescence enhancement induced by ascorbic acid-mediated surface reduction of carbon dots.

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease without cure. Reactive oxygen species (ROS)-induced oxidative stress and mitochondrial dysfunction are considered critical factors in ALS pathogenesis. Here, we design carbon dot superoxide dismutase (SOD) nanozymes with manganese doping (Mn@CDs) by screening for the optimal active site according to the special structures of natural SODs. Mn coordinates with N and O in the CD scaffold, optimizing its structure, enhancing electron transfer and superoxide anion binding, and achieving superhigh specific activity of more than 7×10 ⁴ U/mg. Theoretical calculations reveal the SOD-like activity of Mn@CDs from both kinetic and thermodynamic perspectives, identifying MnN ₂ O ₂ (with amide-derived N) as the most likely active center. Unlike previous single-atom nanozymes with planar structures, this active center exhibits a coordination environment and a non-planar spatial conformation that closely resembles the active site of natural MnSOD enzymes. After being applied in ALS therapy, Mn@CDs effectively prevent oxidative stress and protect mitochondria from abnormalities in morphology, quantity, and function. Hence, administration of Mn@CDs prolonged survival by 14.5 days, with a 93% increase over the effect of edaravone. These results suggest that Mn@CDs hold significant potential as a promising therapeutic candidate for ALS treatment.

A smartphone-assisted ratiometric fluorescence sensor based on green emissive Cu nanoclusters (Cu NCs) and red emissive Ag nanoclusters (Ag NCs) is constructed, in which the Cu NCs and Ag NCs bind with each other through electrostatic interaction, leading to fluorescence resonance energy transfer from Cu NCs to Ag NCs. The copper ions (Cu²⁺) can quench the red fluorescence of the Cu NCs -Ag NCs system, while the green fluorescence remains essentially unchanged, thus enabling the fluorescence ratio detection of Cu²⁺. This method demonstrates high selectivity for Cu²⁺ and a wide detection range (1.0 to 60.0 μM). The limit of detection is as low as 0.36 μM, which is significantly lower than the maximum tolerable concentration in drinking water (~ 20 μM). In addition, the fluorescence color can be converted into RGB values by a smartphone, indicating great potential for point-of-care testing of Cu²⁺ in real water samples. Graphical Abstract

Multienzymatic nanozymes hold great potential in therapeutics due to their higher catalytic efficiency and multifunctionality. However, flexibly switching the antioxidant and prooxidant activities of multienzymic nanozymes at the same lesion remains a challenge. Herein, we design magnesium-doped carbon dot (Mg-CD) nanozymes with photoswitchable antioxidant and prooxidant activities under physiological conditions. The Mg-CD nanozymes exhibit superoxide dismutase (SOD)-like activity and can scavenge singlet oxygen and hydroxyl radicals without illumination. Interestingly, the antioxidant activity can be converted to oxidase-like activity under visible light illumination, producing singlet oxygen and superoxide anions. The mechanism of the switchable activities is attributed to the fact that coordination between magnesium and the CD skeleton enhances the excited-state electron transfer of singlet states and the energy transfer of triplet electrons. Therefore, Mg-CDs can act as antibacterial and anti-inflammatory agents. Mg-CDs exhibit antibacterial rates exceeding 99% within 5 min under illumination. They can scavenge reactive oxygen species, thereby showing excellent capacity in treating inflammatory wounds caused by lipopolysaccharide. These photoswitchable antioxidant and prooxidant activities of CD nanozymes offer an effective strategy for better manipulating the versatility of nanozymes, expanding their intelligent biomedical applications.

Although carbon dots (CDs) are widely used in the detection of heavy metal ions, rationally designing high-performance CDs for metal ion detection remains a significant challenge due to the limited understanding of their interaction mechanism. Here, we reveal the excited-state intramolecular proton transfer (ESIPT) in CDs and provide an effective strategy for switching the ESIPT by coordinating with metal ions. This work demonstrates that Zn²⁺ has strong coordination capacity toward CDs, while Mn²⁺ has the mildest coordination mode that can effectively sense other metal ions. Reasonable design of CDs with unique responses to heavy metal ions is achieved by doping Zn²⁺ or Mn²⁺ to regulate the ESIPT process. Therefore, a fluorescent sensor array for the sensitive identification of 10 kinds of heavy metal ions in real samples is constructed, which shows consistent detection results with ICP-OES. This work deepens the understanding of the fundamental fluorescence mechanism of CDs, opens new avenues for the rational tuning the emissive process, and provides a simple yet reliable platform to design nanoprobes for heavy metal ions as well as other molecules.