An advanced biosensor based on a closed bipolar electrode (BPE)–electrochemiluminescence (ECL) strategy is proposed for cancer cell adhesion, specific recognition, and detection with dual biomarkers. The system consists of a two-channel polydimethylsiloxane (PDMS) chip (sensing channel and reporting channel) connected through a U-shaped indium tin oxide BPE at a glass surface. A sandwich-type cancer cell detection model is developed at the cathode of the BPE with two recognition molecules, folic acid (FA) and an aptamer. On the basis of the high affinity between FA and the folate receptor that is overexpressed at a cancer cell membrane as well as the excellent conductivity of graphene–Au conjugates, this strategy could achieve the sensitive detection of HL-60 cells, with a limit as low as 18 cells in 30 μL of cell suspension. Control experiments confirm that the sandwich assay specifically captures cancer cells and recognizes target cells.

Photoelectrochemical (PEC) biosensing with semiconductor quantum dots (QDs) has received great attention because it integrates the advantages of both photo-excitation and electrochemical detection. During the photon-to-electricity conversion in PEC processes, electron–hole (charge) separation competes with electron–hole recombination, and the net effect essentially determines the performance of PEC biosensors. Herein, we propose a new approach for slowing down electron–hole recombination to increase charge separation efficiency for PEC biosensor development. Through doping with Mn²⁺, a pair of d bands (⁴T₁ and ⁶A₁) is inserted between the conduction and valence bands of CdS QDs, which alters the electron–hole separation and recombination dynamics, allowing the generation of long-lived charge carriers with ms-scale lifetime that decay about 10⁴–10⁵-fold more slowly than in the case of undoped QDs. Photocurrent tests indicated that Mn²⁺ doping resulted in an approximately 80 % increase in photocurrent generation compared with undoped CdS QDs. For application, the Mn-doped CdS QDs were coated on the surface of a glassy carbon electrode and functionalized with a cell surface carbohydrate-specific ligand (3-aminophenylboronic acid). In this way, a sensitive cytosensor for K562 leukemia cells was constructed. Moreover, the sugar-specific binding property of 3-aminophenylboronic acid allowed the electrode to serve as a switch for the capture and release of cells. This has been further explored with a view to developing a reusable PEC cytosensing platform.

Chemical modification with foreign atoms is a leading strategy to intrinsically modify the properties of host materials. Among them, potassium (K) modification plays a critical role in adjusting the electronic properties of carbon materials. Graphene, a true 2D carbon material, has shown fascinating applications in electrochemical sensing and biosensing. In this work, a facile and mild strategy to K-modifying in graphene at room-temperature is reported for the first time. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectra, and cyclic voltammetry are used to characterize this K-modified graphene. The K-modified graphene is capable of acting as an electron transfer medium and more efficiently promotes charge transfer than unmodified graphene. A highly sensitive and stable amperometric sensor based on its excellent electrocatalytic activity toward the oxidation of NO₂⁻ is proposed. The sensor shows a linear range from 0.5 μM to 7.8 mM with a detection limit of 0.2 μM at a signal-to-noise ratio of 3. The modified electrode has excellent analytical performance and can be successfully applied in the determination of NO₂⁻ released from liver cancer and leukemia cells and shows good application potential in biological systems.

A newly developed electrochemical cell sensor for the determination of K562 leukemia cells using 3-aminophenylboronic acid (APBA)-functionalized multiwalled carbon nanotubes (MWCNTs) films is demonstrated. The films are generated by the covalent coupling between the NH₂ groups in APBA and the COOH group in the acid-oxidized MWCNTs. As a result of the sugar-specific affinity interactions, the K562 leukemia cells are firmly bound to the APBA-functionalized MWCNTs film via boronic acid groups. Compared to electropolymerized APBA films, the presence of MWCNTs not only provides abundant boronic acid domains for cell capture, their high electrical conductivity also makes the film suitable for electrochemical sensing applications. The resulting modified electrodes are tested as cell detection sensors. This work presents a promising platform for effective cell capture and constructing reusable cytosensors.

This work describes for the first time signal-on electrochemiluminescence (ECL) enzyme biosensors based on cadmium sulfide nanocrystals (CdS NCs) formed in situ on the surface of multi-walled carbon nanotubes (MWCNTs). The MWCNT–CdS can react with H₂O₂ to generate strong and stable ECL emission in neutral solution. Compared with pure CdS NCs, the MWCNT–CdS can enhance the ECL intensity by 5.3-fold and move the onset ECL potential more positively for about 400 mV, which reduces H₂O₂ decomposition at the electrode surface and increases detection sensitivity of H₂O₂. Furthermore, the ECL intensity is less influenced by the presence of oxygen in solution. Benefiting from these properties, signal-on enzyme-based biosensors are fabricated by cross-linking choline oxidase and/or acetylcholine esterase with glutaraldehyde on MWCNT–CdS modified electrodes for detection of choline and acetylcholine. The resulting ECL biosensors show wide linear ranges from 1.7 to 332 µM and 3.3 to 216 µM with lower detection limit of 0.8 and 1.7 µM for choline and acetylcholine, respectively. The common interferents such as ascorbic acid and uric acid in electrochemical enzyme-based biosensors do not interfere with the ECL detection of choline and acetylcholine. Furthermore, both ECL biosensors possess satisfying reproducibility and acceptable stability.