Chemical Sensing in Process Analysis

A critical review of recent trends, and a future perspective of optical spectroscopy as PAT in biopharmaceutical downstream processing

As competition in the biopharmaceutical market gets keener due to the market entry of biosimilars, process analytical technologies (PATs) play an important role for process automation and cost reduction. This article will give a general overview and address the recent innovations and applications of spectroscopic methods as PAT tools in the downstream processing of biologics. As data analysis strategies are a crucial part of PAT, the review discusses frequently used data analysis techniques and addresses data fusion methodologies as the combination of several sensors is moving forward in the field. The last chapter will give an outlook on the application of spectroscopic methods in combination with chemometrics and model predictive control (MPC) for downstream processes. Graphical abstract.

Proposal for dark exciton based chemical sensors

The rapidly increasing use of sensors throughout different research disciplines and the demand for more efficient devices with less power consumption depends critically on the emergence of new sensor materials and novel sensor concepts. Atomically thin transition metal dichalcogenides have a huge potential for sensor development within a wide range of applications. Their optimal surface-to-volume ratio combined with strong light–matter interaction results in a high sensitivity to changes in their surroundings. Here, we present a highly efficient sensing mechanism to detect molecules based on dark excitons in these materials. We show that the presence of molecules with a dipole moment transforms dark states into bright excitons, resulting in an additional pronounced peak in easy accessible optical spectra. This effect exhibits a huge potential for sensor applications, since it offers an unambiguous optical fingerprint for the detection of molecules—in contrast to common sensing schemes relying on small peak shifts and intensity changes.

Two-dimensional materials have shown great promise as efficient chemical sensors. Here, the authors present a sensing mechanism to allow the detection of molecules based on dark excitons in atomically thin transition metal dichalcogenides.

Air-gating and chemical-gating in transistors and sensing devices made from hollow TiO2 semiconductor nanotubes

Rapid miniaturization of electronic devices down to the nanoscale, according to Moore's law, has led to some undesirable effects like high leakage current in transistors, which can offset additional benefits from scaling down. Development of three-dimensional transistors, by spatial extension in the third dimension, has allowed higher contact area with a gate electrode and better control over conductivity in the semiconductor channel. However, these devices do not utilize the large surface area and interfaces for new electronic functionality. Here, we demonstrate air gating and chemical gating in hollow semiconductor nanotube devices and highlight the potential for development of novel transistors that can be modulated using channel bias, gate voltage, chemical composition, and concentration. Using chemical gating, we reversibly altered the conductivity of nanoscaled semiconductor nanotubes (10-500 nm TiO2 nanotubes) by six orders of magnitude, with a tunable rectification factor (ON/OFF ratio) ranging from 1-10(6). While demonstrated air- and chemical-gating speeds were slow here (∼seconds) due to the mechanical-evacuation rate and size of our chamber, the small nanoscale volume of these hollow semiconductors can enable much higher switching speeds, limited by the rate of adsorption/desorption of molecules at semiconductor interfaces. These chemical-gating effects are completely reversible, additive between different chemical compositions, and can enable semiconductor nanoelectronic devices for 'chemical transistors', 'chemical diodes', and very high-efficiency sensing applications.

Biosensors and bio-based methods for the separation and detection of foodborne pathogens

The safety of our food supply is always a major concern to consumers, food producers, and regulatory agencies. A safer food supply improves consumer confidence and brings economic stability. The safety of foods from farm-to-fork through the supply chain continuum must be established to protect consumers from debilitating, sometimes fatal episodes of pathogen outbreaks. The implementation of preventive strategies like hazard analysis critical control points (HACCP) assures safety but its full utility will not be realized unless supportive tools are fully developed. Rapid, sensitive, and accurate detection methods are such essential tools that, when integrated with HACCP, will improve safety of products. Traditional microbiological methods are powerful, error-proof, and dependable but these lengthy, cumbersome methods are often ineffective because they are not compatible with the speed at which the products are manufactured and the short shelf life of products. Automation in detection methods is highly desirable, but is not achievable with traditional methods. Therefore, biosensor-based tools offer the most promising solutions and address some of the modern-day needs for fast and sensitive detection of pathogens in real time or near real time. The application of several biosensor tools belonging to the categories of optical, electrochemical, and mass-based tools for detection of foodborne pathogens is reviewed in this chapter. Ironically, geometric growth in biosensor technology is fueled by the imminent threat of bioterrorism through food, water, and air and by the funding through various governmental agencies.

Optically-based chemical and biochemical sensors for the detection of some drugs and biological compounds

The development of new methods for determining at a very low level a large spectrum of substances affecting the behaviour of living organisms is still a challenging goal. For such a purpose, chemical sensors which can be defined as the intimate combination of a sensitive and specific layer with a transducer, are undoubtedly among the more promising devices. In this field, optical sensors are expanding rapidly, mainly based on absorption, fluorescence, chemi- and bioluminescence. Beside pH and gases, drugs (anticonvulsant, antitumour, anaesthetic...) and other compounds of biological interest can be determined with specifically designed optical sensors, for instance immunosensors. Special attention will be given to optical biosensors with emphasis on chemi- and bioluminescence-based devices which are highly selective and ultrasensitive. When co-immobilizing various auxiliary enzymes in the sensing layer, the potentialities of such devices can be greatly extended as demonstrated by promising results recently obtained in our group.

Instrumentation in the Next Decade

The progress of instrumentation and measurement science in the next decade will be marked by three major trends. First, as the average instrument achieves a rather considerable level of intelligence, "dumb" systems will become the exception, and we will eventually begin to become proficient in exploiting the resulting capabilities. Second, more sophisticated understanding of measurement science and of actual measurement needs will drive instrumentation design advances such as miniaturized sensors and yet more "hyphenated" instruments and "mapping" instruments. Third, the combination of sensor-based instrumentation and microminiaturization will make possible distributed measurement by allowing point-of-use measurements by nonexperts.

Trends in analytical instrumentation

Methods for deriving chemical information from a variety of systems and environments have changed dramatically in the last decade. Unique principles from physics, chemistry, and biology are the basis for sophisticated instruments that incorporate computers for data acquisition, reduction, and interpretation. Such analytical systems have shown orders-of-magnitude improvements in sensitivity, specificity, and speed, yet with greater simplicity and lower price. The increasing importance of analytical instrumentation requires reexamination of its coverage in educational curricula and of the role of the analytical chemist in its further development and application.