Reliable surface-enhanced Raman scattering (SERS) based biosensing in complex media is impeded by nonspecific protein adsorptions. Because of the near-field effect of SERS, it is challenging to modify SERS-active substrates using conventional nonfouling materials without introducing interference from their SERS signals. Herein, we report a stealth surface modification strategy for sensitive, specific and accurate detection of fructose in protein solutions using SERS by forming a mixed self-assembled monolayer (SAM). The SAM consists of a short zwitterionic thiol, N,N-dimethyl-cysteamine-carboxybetaine (CBT), and a fructose probe 4-mercaptophenylboronic acid (4-MPBA). The specifically designed and synthesized CBT not only resists protein fouling effectively, but also has very weak Raman activity compared to 4-MPBA. Thus, the CBT SAM provides a stealth surface modification to SERS-active substrates. The surface compositions of mixed SAMs were investigated using X-ray photoelectron spectroscopy (XPS) and SERS, and their nonfouling properties were studied with a surface plasmon resonance (SPR) biosensor. The mixed SAM with a surface composition of 94% CBT demonstrated a very low bovine serum albumin (BSA) adsorption (∼3 ng/cm(2)), and moreover, only the 4-MPBA signal appeared in the SERS spectrum. With the use of this surface-modified SERS-active substrate, quantification of fructose over clinically relevant concentrations (0.01-1 mM) was achieved. Partial least-squares regression (PLS) analysis showed that the detection sensitivity and accuracy were maintained for the measurements in 1 mg/mL BSA solutions. This stealth surface modification strategy provides a novel route to introduce nonfouling property to SERS-active substrates for SERS biosensing in complex media.
Titanium and stainless steel materials are widely used in numerous devices or in custom parts for their excellent mechanical properties. However, their lack of biocompatibility seriously limits their usage in the biomedical field. This study focuses on the grafting of triblock copolymers on titanium and stainless steel metal susbtrates for improving their general biofouling resistance. The series of copolymers that we designed is composed of two blocks of zwitterionic sulfobetaine (SBMA) monomers and one block of glycidyl methacrylate (GMA). The number of repeat units forming each block, n, was finely tuned and controlled to 25, 50, 75, or 100, permitting regulation of the grafting thickness, the morphology, and the dependent properties such as the surface hydrophilicity and biofouling resistance. It was shown that the copolymer possessing n = 50 repeat units in each block, corresponding to a molecular weight of about 15.2 kDa, led to the best nonfouling properties, assessed using plasma proteins, blood cells, fibroblasts cells, and various bacteria. This was explained by an optimized grafting degree and chain organization of the copolymer. Lower value (n = 25) and higher values (n = 75, 100) led to low surface coverage and the formation of aggregates, respectively. The best copolymer was grafted onto scalpels (steel) and dental roots (titanium), and antifouling properties demonstrated using Escherichia coli and HT1080 cells. Results of this work show that this unique triblock copolymer holds promise as a potential material for surface modification of biomedical metallic devices, provided a fine-tuning of the blocks organization and length.
Self-cleaning surfaces allow the reversible attachment and detachment of microorganisms which show great promise in regards to their reusability as smart biomaterials. However, a widely used biomaterial such as polydimethylsiloxane (PDMS) suffers from high biofouling activity and hydrophobic recovery that results in decreased efficiency and stability. A current challenge is to modify and fabricate self-cleaning PDMS surfaces by incorporating antifouling and pH-sensitive properties. To address this, we synthesized a zwitterionic and pH-sensitive random poly(glycidyl methacrylate- co-sulfobetaine methacrylate- co-2-(dimethylamino)ethyl methacrylate) polymer, poly(GMA- co-SBMA- co-DMAEMA). In this work, chemical modification of PDMS was done by grafting onto poly(GMA- co-SBMA- co-DMAEMA) after surface activation via UV and ozone for 90 min to ensure the formation of covalent bonds necessary for stable grafting. The PDMS grafted with G20-S40-D40 exhibit antifouling and pH-sensitive properties by mitigating fibrinogen adsorption, blood cell adhesion, and releasing 98% adhered E. coli bacteria after immersion at basic pH. The grafting of poly(GMA- co-SBMA- co-DMAEMA) presented in this work shows attractive potential for biomedical and industrial applications as a simple, smart, and effective method for the modification of PDMS interfaces.
This study develops a multi-functional hydrogel with a dual injection system based on the adhesive and self-healing properties of the byssus excretion found in mussels. Through precisely controlling the composite cross-linking hydrophobic association (HA) structure composed of A and B solutions, a high-strength, temperature-sensitive injectable hydrogel can be obtained, and it has good self-healing properties. The main composition of A solution contains the surfactant SDS, which can form amphiphilic micelles, the strength increasing component stearyl methacrylate (C18), and NIPAAm, which provides thermo-sensitivity. Solution B contains dopamine acrylate (DAA), which has self-healing properties, and ferric chloride (FeCl3), which is a connecting agent. The rheological behavior shows that when the temperature is increased from 25 °C to 32 °C, the gel can be completed in seven minutes to form a composite hydrogel of NIPAAm-DAA-HA. When NMR identification was conducted on composite DAA, it was found that when comparing DAA and dopamine hydrochloride there were new peaks with specific characteristics, which confirm that this study successfully prepared DAA; swelling tests found that swelling could surpass a rate of 100%, and a higher ratio of crosslinking agent decreased the amount of moisture absorbed; the results of the compression test showed that the addition of hydrophobic micelles C18 effectively enhanced the mechanical properties of hydrogel, allowing it to withstand increased external stress; the adhesiveness results show that an increase in the catechol-Fe3+ concentration of the NIPAAm-DAA-HA hydrogel results in an increased adhesiveness of 0.0081 kg/cm2 on pig skin; the self-healing tests show that after taking damage, NIPAAm-DAA-HA hydrogel can be reactivated with catechol-Fe3+ and self-heal at a rate of up to 70% after 24 h; antibacterial tests show that hydrogel has good bacterial resistance to against E. coli, staphylococcus epidermidis, and bacillus cereus; through in vitro transdermal absorption, it can be seen that the release ability of drugs within the hydrogel can reach up to 8.87 μg/cm2. The NIPAAm-DAA-HA hydrogel prepared by this study performed excellently in both adhesion and self-healing tests. The thermo-sensitive and antibacterial properties can be applied to the treatment of deep wounds and address some of the flaws of traditional wound dressings.
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