Competitive Multiple-Mechanism-Driven Electrochemiluminescent Detection of 8‑Hydroxy-2′-deoxyguanosine

Natural selection over billions of years has developed highly effective in vivo signal transduction that is often governed by a series of competitive multiple mechanisms. Several artificial signal transduction pathways have inspired numerous biosensing systems, but most of these are driven by a single mechanism. Herein we describe a multiple-mechanism-driven electrochemiluminescent (ECL) biosensor that utilizes competitive catalytic and steric hindrance effects by assembling hemin/G-quadruplex on carbon nitride nanosheets. Taking the detection of 8-hydroxy-2′-deoxyguanosine (8-OHdG) as example, the dynamic ranges of the detectable concentrations from the different mechanisms were integrated into a single sensor interface. Moreover, the detection sensitivity was more precisely controlled by the competition between the two mechanisms and inherently boosted compared with that of single-mechanism-driven detection. Going beyond the conventional single-mechanism-driven biosensing, the elaborate biomimetic coupling of multiple mechanisms in a single interface may open a new approach for future multiplexed biosensing

Coupled Fluorometer-Potentiostat System and Metal-Free Monochromatic Luminophores for High-Resolution Wavelength-Resolved Electrochemiluminescent Multiplex Bioassay

The sensitive simultaneous detection of multiple biomarkers is critical for the early diagnosis of diseases. Electrochemiluminescence (ECL) offers outstanding advantages, e.g., low background, over other optical sensing techniques. However, multiplexed ECL bioassay is hindered not only by the lack of generally available ECL spectrometers but also by the limited number of biocompatible monochromatic ECL luminophores for decades. Herein, we report addressing these issues by re-examination of the recent tabletop spectrofluorometer coupled potentiostat as a high-resolution ECL spectrum acquisition system and using carbon nitrides as monochromatic luminophores. A wavelength-resolved multiplexing ECL biosensor is demonstrated to simultaneously detect CA19-9 and mesothelin, two pancreatic cancer biomarkers, at a single-electrode interface. This work could initiate new opportunities for more general multiplex ECL biosensors with competitive performances

Highly Sensitive and Quality Self-Testable Electrochemiluminescence Assay of DNA Methyltransferase Activity Using Multifunctional Sandwich-Assembled Carbon Nitride Nanosheets

DNA methylation catalyzed by methylase plays a key role in many biological activities. However, developing a highly sensitive, simple, and reliable way for evaluation of DNA methyltransferase (MTase) activity is still a challenge. Here, we report a sandwich-assembled electrochemiluminescence (ECL) biosensor using multifunctional carbon nitride nanosheets (CNNS) to evaluate the Dam MTase activity. The CNNS could not only be used as an excellent substrate to conjugate a large amount of hairpin probe DNA to improve the sensitivity but also be utilized as an internal reliability checker and an analyte reporter in the bottom and top layers of the biosensor, respectively. Such a unique sandwich configuration of CNNS well coupled the advantages of ECL luminophor that were generally assembled in the bottom or top layer in a conventional manner. As a result, the biosensor exhibited an ultralow detection limit down to 0.043 U/mL and a linear range between 0.05 and 80 U/mL, superior to the MTase activity assay in most previous reports. We highlighted the great potential of emerging CNNS luminophor in developing highly sensitive and smart quality self-testable ECL sensing systems using a sandwiched configuration for early disease diagnosis, treatment, and management

Simultaneous Noncovalent Modification and Exfoliation of 2D Carbon Nitride for Enhanced Electrochemiluminescent Biosensing

As an emerging nitrogen-rich 2D carbon material, graphitic carbon nitride (CN) has drawn much attention for applications ranging from photo-/electro­catalysts to biosensors. Interfacial modification of CN is fundamentally vital but is still in its infancy and remains challenging due to the low reactivity of CN. Here we report that, in conjunction with a π-π stacking interaction, bulk CN could be simultaneously exfoliated via facile mechanical grinding. The obtained CN nanosheets (m-CNNS) not only retained the pristine opto­electronic properties of bulk CN but also enriched a friendly interface for further coupling biomolecules with advanced properties, overcoming the deficiencies of CN in surface science. The m-CNNS were further covalently linked to a DNA probe, and the resultant electro­chemiluminescent biosensor for the target DNA exhibited much enhanced sensitivity with respect to that obtained by direct physical absorption of the DNA probe on unmodified CNNS. This noncovalent exfoliation and interfacial modification should greatly expand the scope of potential applications of CN in areas such as biosensing and should also be applicable to other 2D materials in interface modulation

Metal-Free All-Carbon Nanohybrid for Ultrasensitive Photoelectrochemical Immunosensing of alpha-Fetoprotein

C₆₀ can accept up to six electrons reversibly and show exceptional light absorption over the entire UV–vis spectrum, making it a potential photoactive probe for photoelectrochemical (PEC) bioassay. However, few successful works have been reported to apply fullerenes in PEC biosensing, partially because of the low electronic conductivity and poor interfacial interactions with targeted biomolecules. Herein, we report the addressing of these two obstacles by coupling high conductive graphite flake (Gr), graphene oxide (GO) with sufficient oxygen-containing functional groups, and an alkylated C₆₀ (AC₆₀) into a metal-free all-carbon nanohybrid (AC₆₀-Gr-GO) via harnessing delicate noncovalent interactions among them through a facile mechanical grinding. It was revealed that the as-obtained AC₆₀-Gr-GO nanohybrid not only showed conspicuous enhancement of photocurrent up to 35 times but also offered rich anchors for bioconjugation. With detection of alpha-fetoprotein as an example, the AC₆₀-Gr-GO based PEC immunosensor demonstrated a broad linear detection range (1 pg·mL^–1 to 100 ng·mL^–1) and a detection limit as low as 0.54 pg·mL^–1, superior/competitive to PEC immunosensors for AFP in previous reports. By a proper reinforcement in conductivity and biointerface engineering, this work may provide a new way to use fullerenes as photoactive materials in more general PEC biosensing

Chemically Modulated Carbon Nitride Nanosheets for Highly Selective Electrochemiluminescent Detection of Multiple Metal-ions

Chemical structures of two-dimensional (2D) nanosheet can effectively control the properties thus guiding their applications. Herein, we demonstrate that carbon nitride nanosheets (CNNS) with tunable chemical structures can be obtained by exfoliating facile accessible bulk carbon nitride (CN) of different polymerization degree. Interestingly, the electrochemiluminescence (ECL) properties of as-prepared CNNS were significantly modulated. As a result, unusual changes for different CNNS in quenching of ECL because of inner filter effect/electron transfer and enhancement of ECL owing to catalytic effect were observed by adding different metal ions. On the basis of this, by using various CNNS, highly selective ECL sensors for rapid detecting multiple metal-ions such as Cu²⁺, Ni²⁺, and Cd²⁺ were successfully developed without any labeling and masking reagents. Multiple competitive mechanisms were further revealed to account for such enhanced selectivity in the proposed ECL sensors. The strategy of preparing CNNS with tunable chemical structures that facilely modulated the optical properties would open a vista to explore 2D carbon-rich materials for developing a wide range of applications such as sensors with enhanced performances