Functionalized Graphene Quantum Dots (GQDs) based Label-Free Optical Fluorescence Sensor for CD59 Antigen Detection and Cellular Bioimaging.

Cluster of differentiation (CD59), a cell surface glycoprotein, regulates the complement system to prevent immune damage. In cancer, altered CD59 expression allows tumors to evade immune surveillance, promote growth, and resist certain immunotherapies. Targeting CD59 could enhance cancer treatment strategies by boosting the immune response against tumors. Herein, we present a one-step synthesis of Polyethyleneimine (PEI) functionalized graphene quantum dots (Lf-GQDs) from weathered lemon leaf extract. The fabricated Lf-GQDs were successfully used for the quantitative detection of the cluster of CD59 antigen that is reported for its expression in different types of cancer. In this work, we utilized orientation-based attachment of CD59 antibody (Anti-CD59). Our findings reveal that, instead of using random serial addition of antigen or antibody, oriented conjugation saves accumulated concentration offering greater sensitivity and selectivity. The Anti-CD59@Lf-GQDs immunosensor was fabricated using the oriented conjugation of antibodies onto the Lf-GQDs surface. Besides, the fabricated immunosensor demonstrated detection of CD59 in the range of 0.01 to 40.0 ng mL-1 with a low detection limit of 5.3 pg mL-1. Besides, the cellular uptake potential of the synthesized Lf-GQDs was also performed in A549 cells using a bioimaging study. The present approach represents the optimal utilization of Anti-CD59 and CD59 antigen. This approach could afford a pathway for constructing oriented conjugation of antibodies on the nanomaterials-based immunosensor for different biomarkers detection.

Biofabricated functionalized graphene quantum dots (fGQDs): unraveling its fluorescence sensing mechanism of human telomerase reverse transcriptase (hTERT) antigen andin vitrobioimaging application.

Lung cancer (LC) is a deadly malignancy that is posing a serious threat to human health. Therefore, early detection of LC biomarkers is the key to reducing LC-related fatalities. Herein, we present the first fluorescent-based selective detection of LC biomarker human telomerase reverse transcriptase (hTERT) using polyethyleneimine (PEI) functionalized graphene quantum dots (fGQDs). One-potin situsynthesis of amine-functionalized GQDs was accomplished by hydrothermal carbonization of biowaste-derived cellulose and PEI. Synthesized fGQDs were characterized by various analytical techniques. Synthesized fGQDs not only exhibited enhanced fluorescence life-time but also excellent stability in the different solvents compared to bare GQDs. The surface activation of hTERT-Ab by carbodiimide chemistry (EDC-NHS) resulted in stacking interactions with fGQDs, involving adsorption-desorption as well as competitive mechanisms. The higher inherent affinity of hTERT-Ag (hTERT antigen) for hTERT-Ab (hTERT antibody) resulted in complex formation and recovery of fGQD fluorescence. As a result, this fluorescence sensing demonstrated a greater linear detection range (0.01 ng ml-1-100 µg ml-1) as well as a notable low detection limit (36.3 pg ml-1). Furthermore, the fabricated immunosensor (Ab@fGQDs) has excellent stability and performance in real samples, with an average recovery of 97.32%. The results of cytotoxicity and cellular bioimaging study in A549 cells show that fGQDs can be used for additional nanotherapeutics and biological applications.

Fabrication of Poly-l-lysine-Functionalized Graphene Quantum Dots for the Label-Free Fluorescent-Based Detection of Carcinoembryonic Antigen.

The diagnosis of tumor biomarkers is an attentive approach for the early detection and treatment of cancer. However, a cost-effective, simple, rapid, selective, and sensitive method is a basic prerequisite for diagnostic research. Herein, we present a novel fluorescence-based label-free sensing strategy for the sensitive and selective detection of carcinoembryonic antigen (CEA) using poly-l-lysine (PLL)-functionalized graphene quantum dots (GQDs). The GQDs were synthesized using a greener method by employing carbonized peanut shell (PNS) waste as a carbon source, and functionalization was accomplished using PLL (PLL-GQDs). The fluorescence stability of the PLL-GQDs was tested in a variety of solvent systems and pH solutions. When compared to nonfunctionalized GQDs (PNS-GQDs), prepared PLL-GQDs demonstrated increased fluorescence lifetime, high quantum yield, excellent photostability, biocompatibility, and greater cellular uptake. The PLL-GQDs with abundant surface amine and carboxylic groups showed selective interactions with an activated CEA antibody (CEA-Ab), resulting in the quenching of fluorescence signals. Because of the strong bioaffinity of CEA to the CEA-Ab, the antibody was unwrapped, resulting in the formation of an antibody-antigen complex and the recovery of fluorescence. As a result of this relationship, a turn "on-off-on" sensing mechanism with a strong response to CEA concentration (0.01 ng mL-1 to 100 µg mL-1) and a detection limit of 1.19 pg mL-1 was demonstrated. Furthermore, the fabricated CEA immunosensor (CEA-Ab@PLL-GQDs) performed admirably in real sample analysis, with an average recovery of 98.32%. The cellular uptake performance of PLL-GQDs was also demonstrated in the A427 cell lines, exhibiting a greater cellular uptake potential than PNS-GQDs. The cellular bioimaging study demonstrates that PLL-GQDs can be used for additional therapeutic and biological applications.