Critical review of polymer and hydrogel deposition methods for optical and electrochemical bioanalytical sensors correlated to the sensor’s applicability in real samples

Abstract

Sensors, ranging from in vivo through to single-use systems, employ protective membranes or hydrogels to enhance sample collection or serve as filters, to immobilize or entrap probes or receptors, or to stabilize and enhance a sensor’s lifetime. Furthermore, many applications demand specific requirements such as biocompatibility and non-fouling properties for in vivo applications, or fast and inexpensive mass production capabilities for single-use sensors. We critically evaluated how membrane materials and their deposition methods impact optical and electrochemical systems with special focus on analytical figures of merit and potential toward large-scale production. With some chosen examples, we highlight the fact that often a sensor’s performance relies heavily on the deposition method, even though other methods or materials could in fact improve the sensor. Over the course of the last 5 years, most sensing applications within healthcare diagnostics included glucose, lactate, uric acid, O2, H+ ions, and many specific metabolites and markers. In the case of food safety and environmental monitoring, the choice of analytes was much more comprehensive regarding a variety of natural and synthetic toxicants like bacteria, pesticides, or pollutants and other relevant substances. We conclude that more attention must be paid toward deposition techniques as these may in the end become a major hurdle in a sensor’s likelihood of moving from an academic lab into a real-world product. Graphical abstract

A Simple and Fast Compression‐Based Method to Fabricate Responsive Gold‐pNIPAM Hybrid Materials: From Thin Films to Anisotropic Microgels

“…[ 64 ] Also, the fine thickness modulation of films below tens of microns in thickness represents an advantage of this compression‐based method over other molding‐based or blade‐coating fabrication techniques. [ 65 ]…”

Impact of Tribological Conditions on Collagen Coating Self-Healing

“…A collagen coating was prepared using a protein solution containing a material extracted from the tail of a rat. Figure 1 shows the process of preparing a collagen solution and forming it into a thin film coating [ 22 ]. First, a neutralized collagen solution with a concentration of 2 mg/mL was prepared by mixing 581.4 µL of protein solution with a concentration of 3.44 mg/mL, 100 µL of phosphate buffered saline (PBS) solution, 11.4 µL of 1 M sodium hydroxide (NaOH) solution, and 307.2 µL of deionized (DI) water.…”

Challenges and Advances of Hydrogel-Based Wearable Electrochemical Biosensors for Real-Time Monitoring of Biofluids: From Lab to Market. A Review

“…The process of applying a thin layer of polymers and metal-based nanostructures onto conductive or semiconductive materials can be efficiently and economically achieved through the use of electrochemical deposition methods . As a standard and suitable method for the fabrication of HWEBs, applying a current flow initiates polymerization in a two- or three-electrode system . The working electrode is subjected to an adequate potential or current, often by cyclic voltammetry (CV), amperometry, or potentiometry, to induce the polymerization of precursors on the electrode surface directly.…”

“…76 As a standard and suitable method for the fabrication of HWEBs, applying a current flow initiates polymerization in a two-or three-electrode system. 77 The working electrode is subjected to an adequate potential or current, often by cyclic voltammetry (CV), amperometry, or potentiometry, to induce the polymerization of precursors on the electrode surface directly. The formation of reactive radicals through the oxidation of monomers initiates the polymerization process.…”

“…The electrical conductivity of hydrogels is of prime importance because it significantly influences the electrochemical sensing performance through effective electron transfer between the biological sensing element and the electrode surface . This approach has been used to deposit several conductive polymers such as poly­(acetylene), poly­(ethylene dioxythiophene), poly­(p-phenylenevinylene), poly­(pyrrole), and poly­(aniline) . The electrodeposition method facilitates the in situ formation of a uniform layer of a hydrogel-based electrode on the surface with controlled thickness. , The characteristics of the deposited layer, including the thickness, porosity, and homogeneity, can be adjusted by controlling the applied potential, current, scan rate, temperature, pH, and ionic strength of precursor solutions .…”