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Hydrogels are of great importance for functionalizing sensors and microfluidics, and poly(ethylene glycol) dimethacrylate (PEG-DMA) is often used as a viscosifier for printable hydrogel precursor inks. In this study, 1–10 kDa PEG-DMA based hydrogels were characterized by gravimetric and electrochemical methods to investigate the diffusivity of small molecules and proteins. Swelling ratios (SRs) of 14.43–9.24, as well as mesh sizes ξ of 3.58–6.91 nm were calculated, and it was found that the SR correlates with the molar concentration of PEG-DMA in the ink (MCI) (SR = 0.1127 × MCI + 8.3256, R2 = 0.9692) and ξ correlates with the molecular weight (Mw) (ξ = 0.3382 × Mw + 3.638, R2 = 0.9451). To investigate the sensing properties, methylene blue (MB) and MB-conjugated proteins were measured on electrochemical sensors with and without hydrogel coating. It was found that on sensors with 10 kDa PEG-DMA hydrogel modification, the DPV peak currents were reduced to 92 % for MB, 73 % for MB-BSA, and 23 % for MB-IgG. To investigate the diffusion properties of MB(-conjugates) in hydrogels with 1–10 kDa PEG-DMA, diffusivity was calculated from the current equation. It was found that diffusivity increases with increasing ξ. Finally, the release of MB-BSA was detected after drying the MB-BSA-containing hydrogel, which is a promising result for the development of hydrogel-based reagent reservoirs for biosensing. [ABSTRACT FROM AUTHOR]

Third-generation biosensors use enzymes capable of direct electron transfer (DET) to the sensor surface. They are of interest for continuous glucose monitoring in blood or interstitial fluid, but they are rarely investigated. One reason is the hindered DET of the enzymes to the metallic electrodes. In this publication, a novel method for the immobilization of cellobiose dehydrogenase (CDH) DET enzymes employing conductive poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) inks and a protective polyethylene glycol dimethacrylate (PEG-DMA) hydrogel layer on gold electrodes is reported. This layer stack showed a glucose-specific current response for voltages between −0.2 and 0.4 V in physiological PBS buffer, and enabled interference-less sensing in a solution of acetaminophen, ascorbic acid, dopamine, and uric acid at 0 V. A Michaelis–Menten fit led to a maximum current density (Imax) of 257 ± 7.9 nA/mm2 and a Michaelis–Menten constant (Km) of 28.4 ± 2.2 mM, with a dynamic range of 0.1–20 mM glucose and a limit of detection of 0.1 mM. After 16 h of continuous measurement of 20 mM glucose, the signal decreased to 60% of its initial value. Storage stability was successfully verified until up to 10 days. In summary, this paper shows a simplified approach for the fabrication of third-generation biosensors using CDH-PEDOT:PSS and PEG-DMA hydrogel inks. [ABSTRACT FROM AUTHOR]

A CMOS-compatible integrated four-channel silicon nitride (Si 3 N 4 ) waveguide based Mach-Zehnder interferometric (MZI) sensor platform was realized with the goal to take maximum advantage of the inherent self-referencing property of MZI-sensors with both sensing and reference waveguides exposed to the sample liquid. To study the self-referencing characteristics of the MZI-sensor system, we compared two sensor configurations—an asymmetric MZI configuration, where the reference waveguide was covered by a cladding, and a symmetric MZI configuration, where the reference waveguide was also in contact with the measurement liquid. To enable biomolecular measurements, we developed an inkjet printing procedure for functional polymers (biotin-modified polyethyleneimine (PEI-B) macromolecules), which allows for local functionalization of sensing waveguides in a cost effective mass-fabrication compatible manner. We could show that for high refractive index changes of the measurement liquid (Δn = 0.007) the background signal can be suppressed by a factor of ∼42 for the symmetric MZI configuration compared to the asymmetric MZI configuration. For the characterization of the functional polymer printing procedure we compared locally functionalized asymmetric and symmetric MZIs with non-locally functionalized asymmetric MZIs, which were prepared with silanization/biotinylation based approach. These locally functionalized MZIs where used for the detection of single stranded DNA (150 bp) with concentrations ranging from 2.5 to 100 nM. The limits of detection were 1.9 nM and 1.6 nM for the non-locally and locally functionalized asymmetric MZI-sensors, respectively. The locally functionalized symmetric MZI-sensors had a four times better LOD of 0.4 nM. These results proof the superior performance of symmetric biosensor arrays with locally deposited functional polymers by means of inkjet printing. [ABSTRACT FROM AUTHOR]

We report a new method for detecting human IgG (hIgG) in serum on integrated-optical Mach-Zehnder interferometer biosensors realized in a high index contrast polymer material system. In the linear range of the sensor (5-200 nM) we observed excellent signal recoveries (95-110%) in buffer and serum samples, which indicate the absence of matrix effects. Signal enhancement was reached by using secondary anti-human IgG antibodies, which bind to immobilized target IgGs and allow detecting concentrations down to 100 pM. This polymer based optical sensor is fully compatible with cost-efficient mass production technologies, which makes it an attractive alternative to inorganic optical sensors. [ABSTRACT FROM AUTHOR]

Biotin- and iminobiotin-bonded surfaces obtained by thiol–ene chemistry and subsequent modification with polyamines were characterized with respect to streptavidin-binding capacity and reversibility for photonic biosensing using X-ray photoelectron spectroscopy and Mach–Zehnder-interferometric sensors. The streptavidin–iminobiotin system was exploited for reversible multilayer deposition and determination of affinity constants on each layer. [ABSTRACT FROM AUTHOR]