REVIEW Spectroscopic sensors for in-line bioprocess monitoring in research and pharmaceutical industrial application Jens Claßen 1 & Florian Aupert 1 & Kenneth F. Reardon 2 & Dörte Solle 1 & Thomas Scheper 1 Received: 30 August 2016 /Revised: 20 October 2016 /Accepted: 27 October 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract The use of spectroscopic sensors for bioprocess monitoring is a powerful tool within the process analytical technology (PAT) initiative of the US Food and Drug Administration. Spectroscopic sensors enable the simulta- neous real-time bioprocess monitoring of various critical pro- cess parameters including biological, chemical, and physical variables during the entire biotechnological production pro- cess. This potential can be realized through the combination of spectroscopic measurements (UV/Vis spectroscopy, IR spectroscopy, fluorescence spectroscopy, and Raman spec- troscopy) with multivariate data analysis to obtain relevant process information out of an enormous amount of data. This review summarizes the newest results from science and industry after the establishment of the PAT initiative and gives a critical overview of the most common in-line spectroscopic techniques. Examples are provided of the wide range of pos- sible applications in upstream processing and downstream processing of spectroscopic sensors for real-time monitoring to optimize productivity and ensure product quality in the pharmaceutical industry. Keywords Bioprocess monitoring . Process analytical technology . Spectroscopic sensors . Critical process parameters . In-line monitoring Introduction The process analytical technology (PAT) initiative announced by the US Food and Drug Administration (FDA) in 2004 has encouraged pharmaceutical companies to intensify process understanding and process control during development and manufacturing with the goal of ensuring final product quality [ 1]. PAT was defined in the ICH Q8 guideline as an Bopportunity to develop more flexible regulatory approaches^ [1]. The PAT framework includes process understanding based on scientific background with the aim to monitor and control all critical process parameters (CPPs) that influence critical quality attributes (CQAs) of the final product. The driving forces for PAT implementation are the safeguarding of high-quality products, the enablement of flexible manufacturing with Bstate-of-the-art^ technologies, reduction of failures, lower energy consumption, improved process un- derstanding, better operator safety, and reduced human errors through increased automation and real-time release of batches. All of these factors result in knowledge-based and robust pro- cess performance over the entire life cycle [2]. To achieve these overall goals, PAT involves tools that include multivar- iate data analysis, design of experiments, bioprocess model- ing, and new sensor technologies. PAT is stimulating the biopharmaceutical industry and ac- ademia to increase development and implementation of new analytical technologies such as spectroscopic sensors that al- low process developers and operators to have more knowl- edge of the process and vastly improved process monitoring. This is particularly important in the biopharmaceutical Published in the topical collection Process Analytics in Science and Industry with guest editor Rudolf W. Kessler. * Dörte Solle solle@iftc.uni-hannover.de 1 Institute of Technical Chemistry, Gottfried Wilhelm Leibniz University of Hannover, Callinstraße 5, 30167 Hannover, Germany 2 Department of Chemical Biological Engineering, Colorado State University, 344 Scott Bioengineering, Fort Collins, Colorado 80523-1370, USA Anal Bioanal Chem DOI 10.1007/s00216-016-0068-x