Integration of a Chemical‐Responsive Hydrogel into a Porous Silicon Photonic Sensor for Visual Colorimetric Readout

The incorporation of a chemo‐responsive hydrogel into a 1D photonic porous silicon (PSi) transducer is demonstrated. A versatile hydrogel backbone is designed via the synthesis of an amine‐functionalized polyacrylamide copolymer where further amine‐specific biochemical reactions can enable control of cross‐links between copolymer chains based on complementary target–probe systems. As an initial demonstration, the incorporation of disulfide chemistry to control cross‐linking of this hydrogel system within a PSi Bragg mirror sensor is reported. Direct optical monitoring of a characteristic peak in the white light reflectivity spectrum of the incorporated PSi Bragg mirror facilitates real‐time detection of the hydrogel dissolution in response to the target analyte (reducing agent) over a timescale of minutes. The hybrid sensor response characteristics are shown to systematically depend on hydrogel cross‐linking density and applied target analyte concentration. Additionally, effects due to responsive hydrogel confinement in a porous template are shown to depend on pore size and architecture of the PSi transducer substrate. Sufficient copolymer and water is removed from the PSi transducer upon dissolution and drying of the hydrogel to induce color changes that can be detected by the unaided eye. This highlights the potential for future development for point‐of‐care diagnostic biosensing.     

Live Lymphocyte Arrays for Biosensing

Systems designed to sensitively and accurately detect whole pathogen particles, their components, or other proteins diagnostic of infection or disease are of interest as sensors for biodefense and clinical diagnostics. To this end, we examined the potential of a sensing strategy based on live T‐cell/B‐cell interactions in a biosensor chip format. An approach to fabricate patterned hydrogel microwells functionalized at their bases with antibodies to promote specific immobilization of lymphocytes was developed and used to array single T cells in a regular pattern on a substrate. A sensing platform was created by overlaying arrayed T cells with a confluent layer of antigen‐capturing B cells. In this system, a peptide analyte added to the chip was captured by B cells and physically presented to arrayed T cells by B‐cell‐surface major histocompatibility complex molecules, triggering T cells through their T‐cell receptors. T‐cell recognition of the target peptide was detected by fluorescence measurements of T‐cell intracellular calcium levels, a biochemical read‐out of T‐cell receptor triggering. We demonstrate that this approach allows rapid, sensitive detection of a model peptide analyte, and that T‐cell arrays allow for maximal T‐cell/B‐cell contacts while simultaneously optimizing single‐cell fluorescence detection for analysis of the sensor response. This approach could be of interest for the design of sensing platforms that can detect both peptide fragments and whole intact pathogens, irrespective of surface mutations that might be induced naturally or during “weaponization”.     

Exploring New Frontiers in Total Food Quality Definition and Assessment: From Chemical to Neurochemical Properties

To understand the concept of “total food quality” and how it has evolved, we give a brief historic outline from Pasteur to the recent rise of the globalized market. Nowadays, “total food quality” is clearly a partially objective concept in the sense that it can be defined according to scientific and technological criteria and partly subjective because consumers’ judgments, mainly based on their appraisal, may equally concur in its definition. Food properties contributing to “total food quality” definition and assessment include (1) organoleptic and sensory attributes, (2) food safety, (3) nutritional value, (4) functionality, (5) service and stability, (6) wholesomeness, and (7) psychological factors. Many technological and gastronomic treatments may alter food components, e.g. fats, proteins, and vitamins (the most sensitive to physico-chemical changes in the environment), thus, negatively affecting any one of the aspects of quality in the above list. Specific analytical strategies and sensitive appliances can be utilized both to assess and protect food quality and to correctly conduct and monitor food production. Among the so-called psychological factors, however, there are some molecular aspects that are still elusive, although of enormously great interest. In fact, food can have some psycho-active effects on the consumer, thus, influencing his or her behavior during either pre-ingestive or post-ingestive phases. As studies of psycho-active substances in food seem to be opening up a new scenario in “total food quality” research, the gathering together in a single chart of all the information on the effects of food on its journey, from sight to ingestion, would seem like a good basis for a more rational and thorough discussion of the topic.     

Biochemical Synthesis and Manipulation of a 70 nm DNA Linker for the Assembly of DNA‐Functionalized Gold Nanoparticles

DNA oligonucleotides are extraordinarily well suited as linkers for the programmable assembly of nanoparticles. To extend the scope of DNA‐directed particle assembly, a 70 nm DNA linker molecule for the DNA‐directed assembly of gold nanoparticles is synthesized by biochemical reactions. In particular, polymerase chain reaction (PCR) and subsequent restriction and ligation reactions are employed to synthesize the DNA linker, comprising a 178 base pair (bp) double helical core region supplemented with two sticky‐end binding sites of 12 nucleotides in length, attached to one of the core‐forming strands. The linker is used for the assembly of DNA‐functionalized gold nanoparticles employing yet another biochemical reaction, namely covalent linkage through the enzyme DNA ligase. The resulting nanoparticle assemblies are characterized by using atomic force microscopy. The methodology described here represents a general way of synthesizing programmable DNA linker molecules with dimensions that exceed those presently available by using chemical synthetic methods, and thus, supplements the synthetic toolbox of nanobiotechnology to asses complex and functional nanoparticle/linker architectures for potential applications in sensing and materials science.     

Steady‐State and Transient Behavior of Organic Electrochemical Transistors

In recent years, organic electrochemical transistors (OECTs) have emerged as attractive devices for a variety of applications, particularly in the area of sensing. While the electrical characteristics of OECTs are analogous to those of conventional organic field effect transistors, appropriate models for OECTs have not yet been developed. In particular, little is known about the transient characteristics of OECTs, which are determined by a complex interplay between ionic and electronic motion. In this paper a simple model is presented that reproduces the steady‐state and transient response of OECTs by considering these devices in terms of an ionic and an electronic circuit. A simple analytical expression is derived that can be used to fit steady‐state OECT characteristics. For the transient regime, comparison with experimental data allowed an estimation of the hole mobility in poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate). This work paves the way for rational optimization of OECTs.     

Sensor Array Composed of “Clicked” Individual Microcantilever Chips

A simple technique is described to functionalize a small library of microcantilever (MC) chips presenting varied headgroups. A generic azide monolayer, bound to the MC surface, can be coupled with various alkynes using efficient "click" chemistry. This method is compatible with many functional groups, and novel headgroups are introduced on the MC surface by means of alkynes synthesized via a one‐step reaction. The surface "click" reaction reduces greatly the effort that would be required to synthesize and purify the corresponding functional thiols. This technique represents a convenient complementary tool for Phase‐Shifting Interferometric Microscopy (PSIM) read‐out that has been developed in our group. The affinity of these surface coatings towards different solvents can be estimated by measuring the deflection of the cantilevers. A proof‐of‐concept sensor composed of four individual MC chips presenting different headgroups can unambiguously discriminate the fingerprint response of a nerve‐gas simulant from other solvent vapors.     

Size‐Specific Interactions Between Single‐ and Double‐Stranded Oligonucleotides and Cationic Water‐Soluble Oligofluorenes

An improved synthetic approach was developed for the synthesis of 1,4‐bis[9′,9′‐bis(6″‐(N,N,N‐trimethylammonium)‐hexyl)‐fluoren‐2′‐yl]benzene tetrabromide ( 1a ), 1,4‐bis[9′,9′;9″,9″‐tetra(6″′‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″‐bisfluoren‐2′‐yl] benzene octabromide ( 1b ) and 1,4‐bis[9′,9′;9″,9″;9″′,9″′‐hexakis(6″″‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″,7″,2″′‐trifluoren‐2′‐yl] benzene dodecabromide ( 1c ). These molecules provide a size‐specific series of water‐soluble oligofluorene molecules with increasing numbers of repeat units to model the interactions between cationic conjugated polymers and DNA. Fluorescence quenching and energy‐transfer measurements were performed with 1a – c and single‐stranded (ss) DNA and double‐stranded (ds) DNA, with and without fluorescein (Fl). These studies show that, on a per‐negative‐charge basis, ssDNA quenches the emission of 1a – c more effectively than dsDNA. Furthermore, we show that the energy‐transfer ratios dsDNA–Fl/ssDNA–Fl are dependent on the number of repeat units in 1a – c .     

压电石英晶体生物传感器及其检测方法

压电石英晶体生物传感器是一种生物传感设备,能快速,简单、无需进行任何标记,并且有选择性地对一些生物分子进行实时检测。已在临床检验、疾病诊断、生物医学、环境监测、污染控制、军事、食品安全以及工业等方面得到了广泛的应用。     

New Materials for Chemical and Biosensors

Wide band gap materials such as SiC, AlN, GaN, ZnO, and diamond have excellent properties such as high operation temperature when used as field effect devices and a high resonating frequency of the substrate materials used in piezoelectric resonator devices. Integration of FET and resonating sensors on the same chip enables powerful miniaturized devices, which can deliver increased information about a gas mixture or complex liquid. Examples of sensor devices based on different wide band gap materials will be given.