Emerging Electrochemical Approaches for the Early Detection of Programmed Cell Death

Abstract

Programmed cell death (apoptosis) safeguards tissue homeostasis, and its dysregulation is a hallmark of cancer, neurodegeneration, and immune disorders. Detecting the earliest biochemical signatures of apoptosis therefore offers a route to sharper diagnosis, real-time therapy monitoring, and data-driven drug discovery. Electrochemical biosensors are uniquely suited to this task because they translate molecular recognition events into electrical signals that are rapid, miniaturizable, and inherently compatible with point-of-care formats. Yet their clinical translation is still limited by three persistent hurdles: (i) selective recognition in protein-rich or highly variable matrices, (ii) long-term signal stability under continuous operation, and (iii) a lack of unified analytical performance standards that hampers cross-platform benchmarking. This critical review charts the most recent material, biochemical, and microelectronic innovations that are beginning to erode these barriers, and identifies emerging strategiesfrom nanostructured electrode interfaces to signal processing that could propel electrochemical apoptosis sensing from proof-of-concept prototypes to reliable bedside tools. By aligning unresolved challenges with promising technological solutions, we aim to guide interdisciplinary efforts toward next-generation diagnostics capable of real-time apoptosis surveillance in complex biological settings.

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A flowchart of apoptosis can illustrate its occurrence through three distinct mechanisms.

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Mitochondrial or intrinsic pathway. Activation in this pathway can occur through the initiator proteins upon induction of p53 by DNA damage, or through activation of Bax and Bak upon the conversion of Bid to tBid by caspase -8, -10. Activation at the mitochondrial membrane causes the release of several mitochondrial factors, such as cytochrome c which combines with Apaf-1 and procaspase-9 forming an apoptosome. Procaspase-9 is then converted into its active form, caspase-9, and then can activate caspase-3 or -7 allowing apoptosis to proceed. In addition, EndoG and AIF that stimulate apoptosis independent of caspases are also released. IAP = inhibitor of apoptosis; Apaf-1 = apoptosis activating factor-1; Bcl-2 and Bcl-xL = block the activation of Bax and Bak; Bcl-2 = B-cell lymphoma-2; Smac = second mitochondrial-derived activator of caspases; DIABLO = director inhibitor of apoptosis-binding protein with LOwpI; tBid = truncated Bid; EndoG = endonuclease G; AIF = apoptosis-inducing factor; Bax 1/4 Bcl-2-associated protein x; Bak = Bcl-2-associated protein k. Reprint with permission from the ref Copyright 2010 The Royal Society of Chemistry.

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Extrinsic or death receptor (DR) pathway. The intracellular portion of the DR is known as the death domain (DD). When receptor–ligand complexes get together, they form a death-inducing signaling complex (DISC). This complex brings in and sets up initiator caspase-8 and lets active caspase enzyme molecules into the cytosol. These molecules activate the effector caspases-3 and -7, resulting in nuclear protein cleavage and the initiation of apoptosis. FasL = Fas ligand; TNFR = tumor necrosis factor receptor; FADD = Fas-associated death domain; TRADD = TNF-associated death domain; C-FLIP = FLICE-like inhibitory protein. Reprint with permission from the ref Copyright 2010 The Royal Society of Chemistry.

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(a) A schematic representation of the rSA@MOF@MB preparation process and the underlying principle for electrochemical caspase-3 detection. Reprint with permission from the ref . Copyright 2024 MDPI. (b) Construction of a nanobiotechnology-enabled electrochemical cytosensing platform. Reprint with permission from the ref . Copyright 2014 Elsevier. (c) (A) The spontaneous organization of biotin-Phe monomers into biotin-FNP, followed by the in situ formation of SA-biotin-FNP networks on the electrode surface. (B) Illustration of the biosensor mechanism for caspase-3 activity detection, utilizing SA-biotin-FNP networks for signal amplification. Reprint with permission from the ref . Copyright 2020 Elsevier. (d) Development of the Dual-Signal-Labeled Electrochemical Immunosensor. Reprint with permission from the ref . Copyright 2016 American Chemical Society.

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(a) Diagram showing the location of cytochrome c within the cell, the process of cell death, and the stages involved in the production of an electrochemical aptasensor for cytochrome c detection. Reprint with permission from the ref . Copyright 2022 Spring Nature. (b) Electrochemical sensing mechanism for caspase-3 activity and cell differentiation. Reprint with permission from the ref . Copyright 2021 Spring Nature. (c) (A) Schematic representation of the SiO₂@QDs–ConA nanoprobe preparation using a Layer-by-Layer (LBL) assembly approach. (B) Illustration of the stepwise fabrication process of the electrochemical cytosensing interface. (C) Diagram depicting the externalization of phosphatidylserine residues on the cell membrane surface during apoptosis. (D) Sandwich-type electrochemical strategy for detecting apoptotic cells. Reprint with permission from the ref . Copyright 2011 the American Chemical Society.