Molybdenum disulfide (MoS2) has emerged as a promising material for biosensing applications due to its unique electronic, optical, and chemical properties. As a transition metal dichalcogenide (TMDC), MoS2 exhibits a tunable bandgap, high surface-to-volume ratio, and exceptional biocompatibility, making it well-suited for detecting biomarkers such as glucose, DNA, and proteins. Its layered structure allows for functionalization with biomolecules, while its semiconducting properties enable sensitive electrochemical and optical transduction mechanisms. This article explores the role of MoS2 in biosensors, detailing its material advantages, fabrication techniques, sensing performance, and integration into wearable devices.

The tunable bandgap of MoS2 is a critical factor in its biosensing capabilities. Bulk MoS2 has an indirect bandgap of approximately 1.2 eV, while monolayer MoS2 transitions to a direct bandgap of around 1.8 eV. This property enables efficient light-matter interactions, which are exploited in optical biosensors such as photoluminescence and surface-enhanced Raman spectroscopy (SERS). The bandgap modulation via layer thickness or strain engineering allows optimization for specific wavelengths, enhancing sensitivity to target biomarkers. For electrochemical sensing, the semiconducting nature of MoS2 facilitates electron transfer reactions when functionalized with enzymes or redox probes. The edge sites of MoS2 nanosheets are particularly active for catalytic processes, improving the detection of molecules like glucose when coupled with glucose oxidase.

Surface chemistry plays a pivotal role in MoS2-based biosensors. The basal planes of MoS2 are relatively inert, but defects and edges provide sites for covalent or non-covalent functionalization with biomolecular recognition elements such as antibodies, aptamers, or DNA probes. Sulfur vacancies can be exploited for thiol-based conjugation, while oxygen plasma treatment introduces hydrophilic groups for improved biocompatibility. The high surface area of MoS2 nanosheets increases the density of immobilized bioreceptors, enhancing the likelihood of biomarker binding. For protein detection, MoS2 surfaces can be modified with linkers like carbodiimide chemistry to attach capture antibodies, enabling specific recognition of targets such as cancer biomarkers.

Fabrication techniques for MoS2 biosensors include mechanical exfoliation, chemical vapor deposition (CVD), and liquid-phase exfoliation. Mechanical exfoliation produces high-quality flakes but suffers from low yield, while CVD allows large-area growth of uniform monolayers with precise control over thickness. Liquid-phase exfoliation, using solvents or surfactants, is scalable for solution-processable MoS2 inks, suitable for printing flexible biosensors. Post-synthesis treatments such as annealing or plasma processing can further optimize the material’s electronic and chemical properties. For device integration, MoS2 is often combined with metal electrodes (e.g., gold or graphene) to form field-effect transistors (FETs) or electrochemical cells.

Electrochemical biosensors leveraging MoS2 exhibit high sensitivity due to the material’s favorable electron transfer kinetics. In glucose sensing, MoS2 nanosheets functionalized with glucose oxidase catalyze the oxidation of glucose, generating a measurable current. The limit of detection for such sensors has been reported in the micromolar range, suitable for physiological glucose monitoring. For DNA detection, MoS2 FETs functionalized with probe DNA exhibit conductance changes upon hybridization with target sequences, achieving detection limits as low as femtomolar concentrations. The sharp switching behavior of MoS2 FETs enhances signal-to-noise ratios, critical for low-abundance biomarkers.

Optical biosensors exploit the strong light-matter interaction in MoS2. Photoluminescence quenching occurs when biomarkers bind to the surface, providing a label-free detection mechanism. SERS platforms utilize MoS2’s plasmonic enhancement effects to amplify Raman signals of adsorbed molecules, enabling single-molecule detection in some cases. The optical response can be tuned by adjusting the layer count or applying external stimuli like electric fields, allowing multiplexed detection of different biomarkers.

Integration of MoS2 biosensors into wearable devices requires flexible and stretchable designs. Solution-processed MoS2 inks can be printed onto polymeric substrates like polydimethylsiloxane (PDMS) or polyethylene terephthalate (PET) to create conformal sensors. Wireless readout systems incorporating MoS2-based electrodes enable real-time monitoring of biomarkers in sweat or interstitial fluid. Challenges include maintaining stability under mechanical deformation and minimizing biofouling in continuous use. Encapsulation strategies using ultrathin barrier layers help protect the active MoS2 components while permitting analyte diffusion.

The limit of detection (LOD) for MoS2 biosensors varies by target and transduction method. For glucose, electrochemical sensors achieve LODs around 0.1–10 µM, covering the clinically relevant range. Protein biomarkers like prostate-specific antigen (PSA) can be detected at concentrations as low as 1 pg/mL using MoS2 FETs with antibody functionalization. DNA sensors reach LODs in the femtomolar range due to the high affinity of nucleic acid hybridization and the signal amplification provided by MoS2’s electronic properties. These performance metrics are competitive with conventional biosensing materials while offering advantages in miniaturization and flexibility.

Future developments in MoS2 biosensors may focus on improving selectivity in complex biological fluids, enhancing long-term stability, and enabling mass production via roll-to-roll fabrication. The combination of MoS2 with other nanomaterials, such as gold nanoparticles or graphene, could further improve sensitivity and multifunctionality. Advances in machine learning for data analysis may also enhance the interpretation of sensor outputs in real-world applications.

In summary, MoS2’s tunable bandgap, rich surface chemistry, and compatibility with diverse fabrication methods make it a versatile platform for biomarker detection. Its integration into wearable systems demonstrates potential for personalized healthcare, enabling continuous, non-invasive monitoring of physiological conditions. As research progresses, MoS2-based biosensors are poised to play a significant role in diagnostics and health monitoring.