7.2 Chemical and Biological Nanosensors

Nanosensors are revolutionizing detection across fields. Chemical nanosensors use electrical, optical, or mechanical changes to identify molecules. Biological nanosensors incorporate biological components for highly specific detection of pathogens, biomolecules, and more.

These tiny sensors offer incredible sensitivity and selectivity. They're transforming healthcare with rapid diagnostics, environmental monitoring with pollution detection, and food safety with pathogen sensing. Understanding their types, principles, and performance metrics is crucial for harnessing their potential.

Types and Principles of Chemical and Biological Nanosensors

Types of nanosensors

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• Chemical nanosensors
  • Electrochemical sensors measure electrical changes from chemical reactions
    • Amperometric detect current changes from redox reactions
    • Potentiometric measure voltage changes from ion concentrations
    • Conductometric analyze conductivity shifts from chemical interactions
  • Optical sensors utilize light interactions for detection
    • Surface plasmon resonance (SPR) detects refractive index changes at metal surfaces
    • Fluorescence-based sensors monitor light emission from fluorophores
  • Mechanical sensors detect physical changes from molecular interactions
    • Cantilever-based sensors measure bending from surface stress changes
    • Quartz crystal microbalance (QCM) detects mass changes through frequency shifts
• Biological nanosensors incorporate biological components for detection
  • Enzymatic biosensors use enzymes to catalyze specific reactions
  • Immunosensors employ antibodies for highly specific antigen detection
  • DNA biosensors utilize nucleic acid hybridization for genetic analysis
  • Aptamer-based sensors use synthetic oligonucleotides for molecular recognition
• Target analytes detected by nanosensors
  • Gases affect air quality and industrial processes (CO2, NO2)
  • Ions play crucial roles in biological systems (H+, Na+)
  • Biomolecules indicate health status and cellular functions (glucose, proteins, DNA)
  • Pathogens cause diseases and contamination (bacteria, viruses)

Principles of chemical nanosensors

• Nanowire sensors leverage electrical properties for detection
  1. Functionalize nanowire surface with specific receptors
  2. Analyte binding alters nanowire conductance
  3. Measure conductance change to quantify analyte concentration
  • High surface-to-volume ratio enhances sensitivity
  • Applicable for various analytes (gases, biomolecules)
• Surface plasmon resonance (SPR) sensors use optical phenomena for sensing
  1. Excite surface plasmons at metal-dielectric interface with incident light
  2. Analyte binding shifts resonance angle
  3. Monitor angle change to detect and quantify analyte
  • Enables real-time, label-free detection
  • Widely used in biomolecular interaction analysis

Applications of biological nanosensors

• Healthcare revolutionized through improved diagnostics and monitoring
  • Rapid disease diagnosis reduces time-to-treatment (malaria, influenza)
  • Continuous glucose monitoring enhances diabetes management
  • Drug discovery accelerated by high-throughput screening
  • Point-of-care testing enables on-site diagnostics (pregnancy tests, blood glucose meters)
• Environmental monitoring enhanced for pollution control
  • Detection of air and water pollutants at low concentrations (particulate matter, lead)
  • Heavy metal monitoring in soil and water samples (mercury, cadmium)
  • Tracking pesticides and herbicides in agricultural runoff
• Food safety improved through rapid and sensitive detection
  • Foodborne pathogen detection prevents outbreaks (E. coli, Salmonella)
  • Monitoring of toxins and allergens ensures consumer safety (aflatoxins, peanut proteins)
  • Quality control in food processing enhances product consistency

Performance metrics of nanosensors

• Sensitivity quantifies signal change per unit analyte concentration
  • Expressed as slope of calibration curve
  • Higher sensitivity allows detection of smaller concentration changes
  • Influenced by transducer efficiency and binding affinity
• Selectivity measures ability to distinguish target from interfering substances
  • Determined by receptor specificity and sensor design
  • Cross-reactivity studies assess potential interferences
  • Crucial for accurate measurements in complex samples
• Limit of detection (LOD) represents lowest detectable analyte concentration
  • Calculated using formula $LOD = 3σ/S$
  • σ: standard deviation of blank, S: sensitivity
  • Lower LOD enables detection of trace amounts
• Response time indicates speed of sensor readout
  • Affected by analyte diffusion and binding kinetics
  • Faster response allows real-time monitoring
• Dynamic range spans linear response to analyte concentration
  • Wide range enables quantification across various concentrations
  • Important for versatile sensor applications
• Reproducibility and stability ensure consistent performance
  • Affected by environmental factors and sensor degradation
  • Critical for reliable long-term use and data comparison