Organic Semiconducting Nanoparticles for Biosensor: A Review

Highly bio-compatible organic semiconductors are widely used as biosensors, but their long-term stability can be compromised due to photo-degradation and structural instability. To address this issue, scientists have developed organic semiconductor nanoparticles (OSNs) by incorporating organic semiconductors into a stable framework or self-assembled structure. OSNs have shown excellent performance and can be used as high-resolution biosensors in modern medical and biological research. They have been used for a wide range of applications, such as detecting small biological molecules, nucleic acids, and enzyme levels, as well as vascular imaging, tumor localization, and more. In particular, OSNs can simulate fine particulate matters (PM_2.5, indicating particulate matter with an aerodynamic diameter less than or equal to 2.5 μm) and can be used to study the biodistribution, clearance pathways, and health effects of such particles. However, there are still some problems that need to be solved, such as toxicity, metabolic mechanism, and fluorescence intensity. In this review, based on the structure and design strategies of OSNs, we introduce various types of OSNs-based biosensors with functional groups used as biosensors and discuss their applications in both in vitro and in vivo tracking. Finally, we also discuss the design strategies and potential future trends of OSNs-based biosensors. This review provides a theoretical scaffold for the design of high-performance OSNs-based biosensors and highlights important trends and future directions for their development and application.

Next-Generation Biomaterials for Culture and Manipulation of Stem Cells

Stem cell fate decisions are informed by physical and chemical cues presented within and by the extracellular matrix. Despite the generally attributed importance of extracellular cues in governing self-renewal, differentiation, and collective behavior, knowledge gaps persist with regard to the individual, synergistic, and competing effects that specific physiochemical signals have on cell function. To better understand basic stem cell biology, as well as to expand opportunities in regenerative medicine and tissue engineering, a growing suite of customizable biomaterials has been developed. These next-generation cell culture materials offer user-defined biochemical and biomechanical properties, increasingly in a manner that can be controlled in time and 3D space. This review highlights recent innovations in this regard, focusing on advances to culture and maintain stemness, direct fate, and to detect stem cell function using biomaterial-based strategies.

Immobilization of Growth Factors for Cell Therapy Manufacturing

Cell therapy products exhibit great therapeutic potential but come with a deterring price tag partly caused by their costly manufacturing processes. The development of strategies that lead to cost-effective cell production is key to expand the reach of cell therapies. Growth factors are critical culture media components required for the maintenance and differentiation of cells in culture and are widely employed in cell therapy manufacturing. However, they are expensive, and their common use in soluble form is often associated with decreased stability and bioactivity. Immobilization has emerged as a possible strategy to optimize growth factor use in cell culture. To date, several immobilization techniques have been reported for attaching growth factors onto a variety of biomaterials, but these have been focused on tissue engineering. This review briefly summarizes the current landscape of cell therapy manufacturing, before describing the types of chemistry that can be used to immobilize growth factors for cell culture. Emphasis is placed to identify strategies that could reduce growth factor usage and enhance bioactivity. Finally, we describe a case study for stem cell factor.

Covalent and selective immobilization of GST fusion proteins with fluorophosphonate-based probes

Fluorophosphonate probes covalently immobilize proteins onto solid support by reacting with tyrosine 111 in the GST tag.

Designing Peptide and Protein Modified Hydrogels: Selecting the Optimal Conjugation Strategy

Hydrogels are used in a wide variety of biomedical applications including tissue engineering, biomolecule delivery, cell delivery, and cell culture. These hydrogels are often designed with a specific biological function in mind, requiring the chemical incorporation of bioactive factors to either mimic extracellular matrix or to deliver a payload to diseased tissue. Appropriate synthetic techniques to ligate bioactive factors, such as peptides and proteins, onto hydrogels are critical in designing materials with biological function. Here, we outline strategies for peptide and protein immobilization. We specifically focus on click chemistry, enzymatic ligation, and affinity binding for transient immobilization. Protein modification strategies have shifted toward site-specific modification using unnatural amino acids and engineered site-selective amino acid sequences to preserve both activity and structure. The selection of appropriate protein immobilization strategies is vital to engineering functional hydrogels. We provide insight into chemistry that balances the need for facile reactions while maintaining protein bioactivity or desired release.

A novel fluorescent turn-on biosensor based on QDs@GSH-GO fluorescence resonance energy transfer for sensitive glutathione S-transferase sensing and cellular imaging

A novel fluorescent turn-on biosensor based on fluorescence resonance energy transfer (FRET) from GSH functionalized Mn-doped ZnS QDs to graphene oxide (GO) was constructed to determine glutathione S-transferases (GSTs) in live cells and human urine. The QDs@GSH is adsorbed on the GO surface via hydrogen bonding interaction between the GSH on the surface of QDs@GSH and GO, and as a result, fluorescence quenching of the QDs@GSH takes place because of FRET. The FRET efficiency from QDs@GSH to GO was calculated to be 86.3%. However, in the presence of GSTs, the FRET process could be inhibited by the specific interaction between the GSH on the surface of QDs@GSH and GSTs, which would keep the QDs@GSH far away from the GO surface, leading to the recovery of the fluorescence. The proposed sensor exhibited high sensitivity, selectivity, and excellent specificity in the buffer, live cells and human urine for the detection of GSTs. Under the physiological conditions (pH 7.4), dissociation constants and the detection limit of GST and ATP6 V1F (a GST-tagged protein) were estimated to be 8.0 × 10^-9 M, 2.1 × 10^-10 M and 3.5 × 10^-9 M, 7.2 × 10^-11 M, respectively. The presented method has been successfully utilized for the determination of the GSTs in live cells and human urine without any complicated pretreatment and the recovery was in the range of 80%-90%.

Reversible and oriented immobilization of ferrocene-modified proteins

Adopting supramolecular chemistry for immobilization of proteins is an attractive strategy that entails reversibility and responsiveness to stimuli. The reversible and oriented immobilization and micropatterning of ferrocene-tagged yellow fluorescent proteins (Fc-YFPs) onto β-cyclodextrin (βCD) molecular printboards was characterized using surface plasmon resonance (SPR) spectroscopy and fluorescence microscopy in combination with electrochemistry. The proteins were assembled on the surface through the specific supramolecular host-guest interaction between βCD and ferrocene. Application of a dynamic covalent disulfide lock between two YFP proteins resulted in a switch from monovalent to divalent ferrocene interactions with the βCD surface, yielding a more stable protein immobilization. The SPR titration data for the protein immobilization were fitted to a 1:1 Langmuir-type model, yielding K(LM) = 2.5 × 10(5) M(-1) and K(i,s) = 1.2 × 10(3) M(-1), which compares favorably to the intrinsic binding constant presented in the literature for the monovalent interaction of ferrocene with βCD self-assembled monolayers. In addition, the SPR binding experiments were qualitatively simulated, confirming the binding of Fc-YFP in both divalent and monovalent fashion to the βCD monolayers. The Fc-YFPs could be patterned on βCD surfaces in uniform monolayers, as revealed using fluorescence microscopy and atomic force microscopy measurements. Both fluorescence microscopy imaging and SPR measurements were carried out with the in situ capability to perform cyclic voltammetry and chronoamperometry. These studies emphasize the repetitive desorption and adsorption of the ferrocene-tagged proteins from the βCD surface upon electrochemical oxidation and reduction, respectively.

Aminooxy and Pyridyl Disulfide Telechelic Poly(Polyethylene Glycol Acrylate) by RAFT Polymerization

An efficient method to synthesize telechelic, bio-reactive polymers is described. Homotelechelic polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization in one step by employing bifunctional chain transfer agents (CTAs). A bis-carboxylic acid CTA was coupled to N-BOC-aminooxy ethanol or pyridyl disulfide ethanol resulting in a bis-N-BOC-aminooxy CTA and a bis-pyridyl disulfide CTA, respectively. RAFT polymerization of polyethylene glycol (PEG) acrylate in the presence of both CTAs resulted in a series of polymers over a range of molecular weights (~8.4 kDa to 35.2 kDa; polydispersity indices, PDIs of 1.11 to 1.44) with retention of end-groups post-polymerization. The polymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography (GPC). Conjugations of small molecules and peptides resulted in homotelechelic polymer conjugates.

Combination of integrin-binding peptide and growth factor promotes cell adhesion on electron-beam-fabricated patterns

Understanding and controlling cell adhesion on engineered scaffolds is important in biomaterials and tissue engineering. In this report we used an electron-beam (e-beam) lithography technique to fabricate patterns of a cell adhesive integrin ligand combined with a growth factor. Specifically, micron-sized poly(ethylene glycol) (PEG) hydrogels with aminooxy- and styrene sulfonate-functional groups were fabricated. Cell adhesion moieties were introduced using a ketone-functionalized arginine-glycine-aspartic acid (RGD) peptide to modify the O-hydroxylamines by oxime bond formation. Basic fibroblast growth factor (bFGF) was immobilized by electrostatic interaction with the sulfonate groups. Human umbilical vein endothelial cells (HUVECs) formed focal adhesion complexes on RGD- and RGD and bFGF-immobilized patterns as shown by immunostaining of vinculin and actin. In the presence of both bFGF and RGD, cell areas were larger. The data demonstrate confinement of cellular focal adhesions to chemically and physically well-controlled microenvironments created by a combination of e-beam lithography and "click" chemistry techniques. The results also suggest positive implications for addition of growth factors into adhesive patterns for cell-material interactions.

Protein nanopatterns by oxime bond formation

Patterning proteins on the nanoscale is important for applications in biology and medicine. As feature sizes are reduced, it is critical that immobilization strategies provide site-specific attachment of the biomolecules. In this study, oxime chemistry was exploited to conjugate proteins onto nanometer-sized features. Poly(Boc-aminooxy tetra(ethylene glycol) methacrylate) was synthesized by free radical polymerization. The polymer was patterned onto silicon wafers using an electron beam writer. Trifluoroacetic acid removal of the Boc groups provided the desired aminooxy functionality. In this manner, patterns of concentric squares and contiguous bowtie shapes were fabricated with 150-170-nm wide features. Ubiquitin modified at the N-terminus with an α-ketoamide group and N(ε)-levulinyl lysine-modified bovine serum albumin were subsequently conjugated to the polymer nanopatterns. Protein immobilization was confirmed by fluorescence microscopy. Control studies on protected surfaces and using proteins presaturated with O-methoxyamine indicated that attachment occurred via oxime bond formation.