A novel “on–off–on” fluorescence assay for the discriminative detection of Cu(ii) and l-cysteine based on red-emissive Si-CDs and cellular imaging applications

Abstract

Copper ions (Cu2+) and l-cysteine (l-Cys) in the human body always play critical roles in various physiological processes, while abnormal Cu2+ and l-Cys concentrations in the biological system lead to many diseases.

Carbon Dots for Intracellular Sensing

“…Detection of cysteine in biological systems is a prerequisite for diagnosis and treatment of these diseases at an early stage. Commonly, the CD-based methods for cysteine detection in living cells are based on that cysteine can recover the fluorescence of CDs quenched by metal ions (Cu 2þ , [145] Hg 2þ , [146,147] Cr(VI), [148] Fe 3þ , [149] and Ag þ [13,14,150,151] ), gold NPs (AuNPs), [152,153] and pH. [94] Metal ions can effectively bind to the surface of CDs via electrostatic interaction and remarkably quench the CD fluorescence due to electron transfer process.…”

“…For instance, Zan et al synthesized Si‐CDs with red fluorescence using APTES ((3‐aminopropyl)triethoxysilane) and neutral red (NR) by hydrothermal treatment. [ 145 ] Si‐CDs contained amino groups that can interact with Cu 2+ to form cupric amine complexes (Si‐CDs@Cu 2+ ), leading to the fluorescence reduction of Si‐CDs. With the addition of l ‐Cys into the Si‐CDs@Cu 2+ system, the fluorescence intensity of Si‐CDs was efficiently restored, which was ascribed to the higher affinity of l ‐Cys for Cu 2+ than that for Si‐CDs.…”

Recent progress in 0D optical nanoprobes for applications in the sensing of (bio)analytes with the prospect of global health monitoring and detailed mechanistic insights

“…83 CQDs are beneficial for sensing applications towards the detection of various bio-analytes including lysine, vitamin B2 (riboflavin), intracellular pH, Fe 3+ , hypochlorite (ClO − ), bilirubin (BR), vitamin B12 (cyanocobalamin), polysaccharide, ATP, cysteine (Cys), homocysteine (Hcy), glutathione (GSH) etc (Table 1). 62 a ,63–82,84–90,93 The sensing phenomenon by CQDs mostly relies on PET, FRET, IFE, static and dynamic quenching. In the case of static quenching, a non-fluorescent ground state complexation is observed via the interaction of CQDs with the quencher, which can be easily examined by UV-Vis absorption spectroscopy or lifetime values.…”

“…Again, Li, Dong and Liu et al designed Si-doped carbon dots (Si-CDs) with red emission via a simple hydrothermal strategy, which exhibited a “ on–off–on ” fluorescence response for the specific detection of l -cysteine with a limit of detection of 0.14 μM and linear range of 0–24 μM for l -Cys. 79 The surface-functionalized amino group of the nanosensor initially underwent chelation with Cu 2+ to form Si-CDs@Cu 2+ , which resulted in fluorescence quenching through the electron transfer mechanism. Upon the addition of l -cysteine to the above-mentioned system, the fluorescence of Si-CDs@Cu 2+ was recovered because of the strong affinity of Cu 2+ towards the l -cysteine ( l -Cys) residue, resulting in the highly specific detection of l -Cys.…”

Carbon Dots: An Insight into Their Application in Heavy Metal Sensing

“…Liu and co-workers synthesized Si-doped CDs using a fluorescent "on-off-on" mode for the detection of Cu 2+ and Lcysteine (L-Cys), wherein, upon recognition of Cu 2+ , the fluorescence was quenched by an electron transfer process. However, fluorescence could be recovered by the addition of L-Cys (Table 1, ref [71]).…”