Figure 2. Detection of Salmonella is based on antibody (HRP-Ab2) binding on bacteria and bio-catalyzed precipitation by horseradish peroxidase. Binding of several HRP-Ab2 on one bacteria cause exponential amplification of the signal.

Contamination of food by pathogenic bacteria is a serious threat to human health and thus biosensors for fast and accurate food quality control are extensively studied. 

Multi-Parametric Surface Plasmon Resonance (MP-SPR) based biosensor was developed to detect Salmonella Typhimurium in dairy products. Direct label-free detection of bacteria by using a capture antibody was further improved utilizing bio-catalyzed precipitation. For control samples the limit of detection (LOD) was 102 CFU/mL and for real samples (powdered milk) LOD was 103 CFU/mL, demonstrating a high sensitivity of the biosensor.

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Figure 1. (A) Binding of stem cells (AD-MSC) on ceramic hydroxyapatite surface was determined for orthopedic prosthesis development. (B) Binding of breast cancer cells (MCF7) to target peptide was measured to develop biosensor for cancer detection from blood sample.

Implants are covered with proteins and cells when introduced into the body. To understand interactions on these interfaces, in vitro tools are utilized. Real-time label-free platforms allowing dynamic and static flow-conditions are exploited to understand cell adhesion and in this way improve compatibility of implants. The same features are advantageous also for biosensor development based on cell detection. Cells can also be used as an analyte in a clinical biosensor (for cancer) study.

Attachment of human mesenchymal stem cells (AD-MSC) and lysozyme protein on a few tens of micrometers thick hydroxyapatite (HA), coated by plasma spraying, was measured by Multi-Parametric Surface Plasmon Resonance (MP-SPR). Hydroxyapatite is a component present in tooth and bone and in its synthetic form it is widely used in orthopedic prosthesis to enhance implant osseointegration (connection to a living bone). The results of MP-SPR measurements showed that cells favor binding on HA coating as opposed to gold.

In a separate experiment, a biosensor was developed to detect tumor cells. Binding of breast cancer cells (MCF7) and non-cancerous cells (MCF-10A) to a surface bound targeting peptide (18-4) and a reference peptide were measured. The biosensor surface was able to distinguish cancer cells from normal cells.

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Figure 1. (A) Multi-Parametric Surface Plasmon Resonance (MP-SPR) measuring the binding of nanoparticles to surface immobilized molecules: Binding of block copolymer micelles (LMP) to mucin surfaces was studied for muco-adhesive ocular drug delivery. (B) Binding of molecules to surface attached nanoparticles: Binding of the opsonizing agent C3b to modified liposome-based nanoparticles was studied to assess nanocarrier immune response.

Nanocarriers are being extensively studied as drug delivery systems for cancer and gene therapy amongst others. Block copolymeric micelles (LMP) were developed as mucoadhesive ocular drug delivery vehicles. Micelles and chitosan interaction parameters on mucin surface were determined using Multi-Parametric Surface Plasmon Resonance (MP-SPR). Micelles adhesion was found to increase slightly with increasing phenylboronic acid (PBA) content of the nanoparticle.

In a separate study, binding of C3b molecules to liposomes was measured using MP-SPR. C3b is part of the innate immune system and it serves as an opsonizing agent enhancing phagocytosis (more specifically tagging the cell for phagocytosis). The affinity of C3b on PEGylated oligo-guanidyl lipid modified (OGP + PEG) liposomes was KD = 7.2 × 10−8 M and surface mass density Γ = 120 – 200 ng/cm2. The binding level was higher on liposomes without PEG.

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Figure 1. Schematic view of the adsorption of block copolymers onto nanocellulose surfaces and of serum components onto the poly(ethylene glycol) polymer brushes, as studied using MP-SPR.

Polymers are extensively studied and often interactions play a key role in the product functionality. Two separate polymer interaction studies were conducted using label-free real-time Multi-Parametric Surface Plasmon Resonance (MP-SPR). Functionalization of nanocellulose surfaces was performed by adsorption of block copolymers. The efficacy of anti-fouling of the PEG-based polymer brushes was quantified by measuring adsorption of serum samples. Based on the MP-SPR measurements, polymers were further characterized in terms of thickness andadsorbed mass. Nanocellulose functionalization was confirmed to be successful and -OH terminated 10 kDa PEG was found to be the best anti-fouling coating, producing 99% resistance.

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