Optical assay of trypsin using a one-dimensional plasmonic grating of gelatin-modified poly(methacrylic acid)

Designable Poly(methacrylic Acid)/Silver Cluster Ring Arrays as Reflectance Spectroscopy-Based Biosensors for Label-Free Plague Diagnosis

A hole array was fabricated via photolithography to wet the bottoms of holes using oxygen plasma. Amide-terminated silane, a water immiscible compound before hydrolysis, was evaporated for deposition on the plasma-treated hole template surface. The silane compound was hydrolyzed along the edges of circular sides of the hole bottom to form a ring of an initiator after halogenation. Poly(methacrylic acid) (PMAA) was grafted from the ring of the initiator to attract Ag clusters (AgCs) as AgC-PMAA hybrid ring (SPHR) arrays via alternate phase transition cycles. The SPHR arrays were modified with a Yersinia pestis antibody (abY) to detect the antigen of Yersinia pestis (agY) for plague diagnosis. The binding of the agY onto the abY-anchored SPHR array resulted in a geometrical change from a ring to a two-humped structure. The reflectance spectra could be used to analyze the AgC attachment and the agY binding onto the abY-anchored SPHR array. The linear range between the wavelength shift and agY concentration from 30 to 270 pg mL^-1 was established to obtain the detection limit of ~12.3 pg mL^-1. Our proposed method provides a novel pathway to efficiently fabricate a ring array with a scale of less than 100 nm, which demonstrates excellent performance in preclinical trials.

LSPR Sensing of Epithelial Cell Adhesion Molecules through Sphere and Cavity Plasmons of a Composite Ring Array of Poly[2-(dimethylamino)ethyl methacrylate]/Gold Nanoparticles

Self-organization facilitates the formation of specific structures as a result of constituent interactions. In this study, the bottom of a 600 nm hole array photoresist template, which was deposited with a hydrophobic atom transfer radical polymerization (ATRP) initiator, was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) was grafted from the ring array of the initiator to immobilize gold nanoparticles (AuNPs) as a uniform ring array on a silicon substrate via repeated swelling/shrinking cycles. The localized surface plasmon resonance (LSPR) peak of the PDMAEMA-AuNP hybrid ring (PAHR) red-shifted after 12 swelling/shrinking cycles. In comparison to gold nanoparticles, scalable gold nanorings can effectively develop a variety of nanostructures to design LSPR-based sensors and optimize the sensing accuracy and stability. To detect epithelial cell adhesion molecules (EpCAM) during the structural change from a ring to a disk, antiEpCAM was anchored onto the PAHR as a biosensor during swelling/shrinking. The coupling of antiEpCAM and EpCAM led to asymptotical convergence from rings to disks as well as blue shifts of the LSPR peaks. Linear correlation between the blue shift and EpCAM concentration showed a limit of detection of ∼27 pg mL^-1 and a linear range of 25-200 pg mL^-1 for the detection of EpCAM within 30 min. The simple method of combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of AuNPs for highly sensitive and selective biosensing.

Inflammation-Responsive Nanovalves of Polymer-Conjugated Dextran on a Hole Array of Silicon Substrate for Controlled Antibiotic Release

Poly(methacrylic acid) (PMAA) brushes were tethered on a silicon surface possessing a 500-nm hole array via atom transfer radical polymerization after the modification of the halogen group. Dextran-biotin (DB) was sequentially immobilized on the PMAA chains to obtain a P(MAA-DB) brush surrounding the hole edges on the silicon surface. After loading antibiotics inside the holes, biphenyl-4,4′-diboronic acid (BDA) was used to cross-link the P(MAA-DB) chains through the formation of boronate esters to cap the hole and block the release of the antibiotics. The boronate esters were disassociated with reactive oxygen species (ROS) to open the holes and release the antibiotics, thus indicating a reversible association. The total amount of drug inside the chip was approximately 52.4 μg cm⁻², which could be released at a rate of approximately 1.6 μg h⁻¹ cm⁻² at a ROS concentration of 10 nM. The P(MAA-DB) brush-modified chip was biocompatible without significant toxicity toward L929 cells during the antibiotic release. The inflammation-triggered antibiotic release system based on a subcutaneous implant chip not only exhibits excellent efficacy against bacteria but also excellent biocompatibility, recyclability, and sensitivity, which can be easily extended to other drug delivery systems for numerous biomedical applications without phagocytosis- and metabolism-related issues.

Facile Molecular Weight Determination of Polymer Brushes Grafted from One-Dimensional Diffraction Grating by SI-ATRP Using Reflective Laser System

Gelatin was immobilized selectively on the amide groups-modified bottom of a trench array of a photoresist template with 2 μm resolution by the ethyl(dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide reaction. The gelatin-immobilized line array was brominated to generate a macroinitiator for atom transfer radical polymerization. Poly(methacrylic acid) (PMAA) brushes were grafted from the macroinitiator layer as line arrays of one-dimensional diffraction gratings (DGs) for various grafting polymerization times. A laser beam system was employed to analyze the optical feature with a characteristic diffraction effect of the PMAA DGs at a 45° incident angle along the transverse magnetic and transverse electric polarization. The growth of the PMAA brush lines increased both their heights and widths, leading to a change in the reflective diffraction intensity. The PMAA brushes under various grafting polymerization times were cleaved from the substrate by digestion of gelatin with trypsin, and their molecular weights were obtained by gel permeation chromatography. The change degree of the diffraction intensity varied linearly with the molecular weight of the PMAA brushes over a wide range, from 135 to 1475 kDa, with high correlation coefficients. Molecular weight determination of polymer brushes using the reflective diffraction intensity provides a simple method to monitor their growth in real time without polymer brush cleavage.

Plasmonic Gold Nanoisland Film for Bacterial Theranostics

Plasmonic nanomaterials have been intensively explored for applications in biomedical detection and therapy for human sustainability. Herein, plasmonic gold nanoisland (NI) film (AuNIF) was fabricated onto a glass substrate by a facile seed-mediated growth approach. The structure of the tortuous gold NIs of the AuNIF was demonstrated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Based on the ultraviolet-visible spectrum, the AuNIF revealed plasmonic absorption with maximum intensity at 624 nm. With the change to the surface topography created by the NIs, the capture efficiency of Escherichia coli (E. coli) by the AuNIF was significantly increased compared to that of the glass substrate. The AuNIF was applied as a surface-enhanced Raman scattering (SERS) substrate to enhance the Raman signal of E. coli. Moreover, the plasmonic AuNIF exhibited a superior photothermal effect under irradiation with simulated AM1.5 sunlight. For photothermal therapy, the AuNIF also displayed outstanding efficiency in the photothermal killing of E. coli. Using a combination of SERS detection and photothermal therapy, the AuNIF could be a promising platform for bacterial theranostics.

Peptide modified manganese-doped iron oxide nanoparticles as a sensitive fluorescence nanosensor for non-invasive detection of trypsin activity in vitro and in vivo

Herein, a fluorescence turn-on nanosensor (MnIO@pep-FITC) has been proposed for detecting trypsin activity in vitro and in vivo through covalently immobilizing an FITC modified peptide substrate of trypsin (pep-FITC) on manganese-doped iron oxide nanoparticle (MnIO NP) surfaces via a polyethylene glycol (PEG) crosslinker. The conjugation of pep-FITC with MnIO NPs results in the quenching of FITC fluorescence. After trypsin cleavage, the FITC moiety is released from the MnIO NP surface, leading to a remarkable recovery of FITC fluorescence signal. Under the optimum experimental conditions, the recovery ratio of FITC fluorescence intensity is linearly dependent on the trypsin concentration in the range of 2 to 100 ng mL-1 in buffer and intracellular trypsin in the lysate of 5 × 102 to 1 × 104 HCT116 cells per mL, respectively. The detection limit of trypsin is 0.6 ng mL-1 in buffer or 359 cells per mL HCT116 cell lysate. The MnIO@pep-FITC is successfully employed to noninvasively monitor trypsin activity in the ultrasmall (ca. 4.9 mm3 in volume) BALB/c nude mouse-bearing HCT116 tumor by in vivo fluorescence imaging with external magnetic field assistance, demonstrating that it has excellent practicability.