Functional Surfaces for Pathogen Detection & Targeting
Bacterial infections continue to be a major public health concern, made worse by the rise of multidrug-resistant strains. Many pathogens rely on glycan recognition for adhesion onto cell surfaces, and must maintain this affinity in order to remain virulent. We exploit this immutable recognition by using glycan-based ligands to support a fault-tolerant platform for pathogen detection (with Phil Low & Ron Reifenberger, Purdue). Synthetic glycoconjugates are printed into periodic arrays for mediating bacterial adhesion at low densities, and imaged under darkfield conditions. A positive identification is made by the emergence of a periodic optical pattern, which can be converted into peak frequency signals by Fourier transform. We have recently demonstrated this method in the detection of Pseudomonas at 1000 cfu/mL.
Capture of live Pseudomonas on a glycan-patterned slide. Demodulation of periodic patterns by FFT produces fault-tolerant signals for positive pathogen detection.
Gold-coated chips are the substrate of choice for ligand presentation, but surface stability depends strongly on the method of surface functionalization. This practical issue is often overlooked yet is critical to the success of the intended application, particularly those involving aqueous media. We have found dithiocarbamates (DTCs) to be strongly chemisorptive ligands on Au substrates, and can be produced in situ by the condensation of amines with CS2. DTC-anchored monolayers (DAMs) are highly resistant to desorption or oxidative degradation, and provide a robust alternative to the more commonly used self-assembled monolayers (SAMs) based on alkanethiols. This surface chemistry has been applied to both Au substrates for pathogen and protein detection, and also for the targeted delivery of nanoparticles.