What is a Biosensor?

Biosensor Definition

Although the term “biosensor” may seem quite clear on first glance, its meaning is less straightforward. A linguist might say a biosensor is a device that “senses life”, as its etymology would suggest. A biologist on the other hand would argue that the term “life” is too broad, while a physicist would likely be confused by the meaning of “sensing”. The question then is: What is a biosensor?



A Definition for All

One of many official definitions states that a biosensor is “a device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles or whole cells to detect chemical compounds” (IUPAC definition). Put simply, this means that a biosensor utilizes molecular interactions from or based on those in living systems to detect a compound of interest. 

There is a myriad of ways to accomplish this, which is why finding a definition that suits all possible biosensors is a challenging task. There are however three basic elements all biosensors have: 

  • a bioreceptor: any biological compound capable of detecting the compound of interest (aka “analyte”, cf. figure). Typical examples include biomolecules such as enzymes, antibodies, but also living organisms such as cells.
  • a signal processor: the part of the biosensor that will convert the physicochemical signal from the receptor to a quantifiable signal we can interpret.
  • a transducer: the part of the biosensor that will link the bioreceptor detecting the compound to the signal processor.


Label vs. Label-Free Biosensors

Biosensors can be classified according to various parameters, such as what type of bioreceptor they use, what transduction type, or what signal processing mechanism they use. Although these classifications can be very useful, they don’t always provide the most practical information. One broader way to categorize biosensors is by separating them into two big classes.

Label biosensors detect the presence and/or activity of molecules of interest thanks to a special tag, the label, that is attached to them. A typical example of such a sensing technology is ELISA (enzyme-linked immunosorbent assay). On the other hand, label-free biosensors detect the presence and/or activity of molecules of interest based on their biophysical properties, such as molecular weight, refractive index (e.g. surface plasmon resonance) or charge. Other examples of label-free technologies include the microcantilever, quartz crystal microbalance and mass spectroscopy. 

What is a label? 

Think of a label as a type of tag for molecules. When you go shopping, each clothing item has a tag with a barcode; this is necessary because a store usually has several copies of the same item. Tags with barcodes allow differentiation of identical items amongst each other, which thereby allows stores to keep track of the number of items they have and the location of each item. Labels in biosensors have a similar function: they help us follow or detect a molecule of interest, so we can distinguish it from the others. In biosensors, the most common way to label a molecule is  by attaching a color tag, most often in the form of fluorescent molecules.  

Beyond simple molecule distinction, labels also enable molecule detection in a simple, visible manner. Indeed, labels provide signal amplification. If the label is attached to an enzyme specific for a molecule of interest, this enzyme can create multiple copies of the color tag every time it binds its specific target molecule. In short, this means one specific binding event will lead to multiple copies of the color tag molecule, which makes it much easier to detect the analyte of interest. 


Which is better?

Using a label is a seemingly smart and practical way to keep track of and detect the molecules we are interested in; however, in biosensing, this isn’t necessarily the case. Indeed, adding labels can cause problems in accurate and precise detection. Firstly, the labels we use are molecules themselves, and these tend to be quite chunky molecules. This means that by attaching them to the molecules we are interested in, we create a much larger and different molecule: this alters the intrinsic properties of the molecule of interest, thereby affecting its transport, activity, and sometimes also its effect. In short, by adding a label, we may not be measuring what we want to measure… Furthermore, adding labels always involves an additional and non-straightforward step in the preparation/fabrication of the biosensor and requires isolation and purification of the molecules of interest. 

This is why label-free technologies are often the preferred strategy for biosensing where one is interested in the thermodynamic properties rather than the identity of the molecule or the concentration of the molecule.  


What concrete examples of label and label-free biosensors are there? How do these biosensors work, and what are their functions? Stay tuned and read more about these questions in the next blog article.

The Concept of a Spatial Affinity Lock-in Amplifier


11. January 2021

Focal molography – a new method for Biomolecular Interaction Analysis (BIA).
The paper introduces and demonstrated the concept of the “spatial affinity lock-in” as a novel design principle to overcome the drawbacks of established BIA methods.The spatial affinity lock-in is analogous to the time-domain lock-in. Instead of a time-domain signal, it modulates the binding signal at a high spatial frequency to separate it from the low spatial frequency environmental noise in Fourier space. Focal molography applies this fundamental detection principle to BIA. Combined with the right surface chemistry and recognition elements on the sensor surface focal molography enables robust, sensitive and fundamentally new BIA assays such as the direct and label-free monitoring of biomolecular interaction on the cell membrane.
Read more about ultra-stable molecular sensors by sub-micron referencing and why they should be interrogated by optical diffraction in our latest paper.

Ultra Stable Molecular Sensors by Submicron Referencing and Why They Should Be Interrogated by Optical Diffraction—Part II. Experimental Demonstration


22. December 2020

Label-free optical biosensors are an invaluable tool for molecular interaction analysis. Over the past 30 years, refractometric biosensors and, in particular, surface plasmon resonance have matured to the de facto standard of this field despite a significant cross reactivity to environmental and experimental noise sources. In this paper, we demonstrate that sensors that apply the spatial affinity lock-in principle (part I) and perform readout by diffraction overcome the drawbacks of established refractometric biosensors. We show this with a direct comparison of the cover refractive index jump sensitivity as well as the surface mass resolution of an unstabilized diffractometric biosensor with a state-of-the-art Biacore 8k. A combined refractometric diffractometric biosensor demonstrates that a refractometric sensor requires a much higher measurement precision than the diffractometric to achieve the same resolution. In a conceptual and quantitative discussion, we elucidate the physical reasons behind and define the figure of merit of diffractometric biosensors. Because low-precision unstabilized diffractometric devices achieve the same resolution as bulky stabilized refractometric sensors, we believe that label-free optical sensors might soon move beyond the drug discovery lab as miniaturized, mass-produced environmental/medical sensors. In fact, combined with the right surface chemistry and recognition element, they might even bring the senses of smell/taste to our smart devices.

lino Biotech closes seed financing round - Businesswire

lino Biotech closes seed financing round and showcases a novel label-free biosensor platform for innovate modern drug screening

lino Biotech

ZURICH–(BUSINESS WIRE)–After almost a decade of initial invention and joint research on the Focal Molography technology at Roche, a leading player in the diagnostics and pharmaceutical area, and ETH Zurich as one of Europe’s most renowned research institutes, lino Biotech AG has licensed the technology to further develop and commercialize Focal Molography. The company has received 7-digit financing from lead-investors HTGF, Roche Ventures and several family offices.

“Molography offers the chance to combine several assays into one single measurement of living cells, thus delivering distinguish information on target specific interactions and shorting development times for novel drugs”

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This broadly patented technology offers label-free detection assays using the power of molecular diffraction while eliminating disturbances of environmental factors such as changes in temperature or non-specific binding. lino’s biosensor platform offers industry customers and researchers a unique way to study molecular interactions in living cells and crude biosystems. Importantly, its broad application spectrum can for the first time, measure drug binding to transmembrane proteins while simultaneously observe intracellular signaling. Additional applications can be found in bioprocessing. With access to modern clean room facilities, the company currently offers its services to selected industry partners as contract research service.

Dr. Mirko Stange, CEO of lino Biotech “experiments with pharma partners have highlighted the value of Focal Molography. However, we are still at the beginning to understand the value of Molography for different industries. For example, we currently evaluate the potential of monitoring multiple parameters in bioreactors as well as another pharma case of measuring high-affinity drug-target interactions in real-time over several days. Two very different applications for different customers that both seem feasible with the technology at hands”.

Dr. Martin Pfister, Principle at HTGF: “Molography offers the chance to combine several assays into one single measurement of living cells, thus delivering distinguish information on target specific interactions and shorting development times for novel drugs”.

For the first time ever, the company will exhibit its biosensor platform and new performance data at the digital DxPx Investor conference from November 17th to 21st


About lino Biotech AG:

lino Biotech AG – www.lino-biotech.com – was incorporated as a ETH Zurich spin-out in Zürich, Switzerland, in March 2020, and is venture backed by Roche Venture Fund, High-Tech Gründerfonds and several lifescience family offices. lino offers industry partners and researchers a unique way to study molecular interactions in living cells and crude biosystems.

About High-Tech Gründerfonds

High-Tech Gründerfonds (HTGF) is a seed investor that finances high-potential, tech-driven start-ups. With around EUR 900 million in total investment volume across three funds and an international network of partners, HTGF has already helped forge almost 600 start-ups since 2005. Driven by their expertise, entrepreneurial spirit and passion, its team of experienced investment managers and startup experts help guide the development of young companies. HTGF’s focus is on high-tech start-ups in the fields of digital tech, industrial technology, life sciences, chemistry and related business areas. To date, external investors have injected over EUR 2.7 billion into the HTGF portfolio via more than 1,600 follow-on financing rounds. HTGF has also successfully sold interests in more than 100 companies.

Investors in the public-private partnership include the Federal Ministry of Economics and Energy, KfW Capital, the Fraunhofer-Gesellschaft and 32 companies. The Fund Investors


lino Biotech AG
Dr. Mirko Stange
Email: m.stange@lino-biotech.com

Press contact
Wordstatt GmbH
Dagmar Metzger

High-Tech Gründerfonds Management GmbH
Martin Pfister, Principal/ Authorized Signatory

Focal Molography – an optical method for label-free detection of biomolecular interactions


1. October 2020

Focal molography is a new method for label-free molecular interaction analysis in crude samples. In contrast to refractometric optical sensors, focal molography is insensitive to nonspecific molecular interactions. This unique property is achieved with a special 2D nanopattern of molecular binding sites on a chip, termed mologram. A mologram is designed such that molecules bound to it diffract light constructively into a focal spot. The intensity of the focused light is measured to quantify the amount of bound molecules. In biological samples, highly abundant off-target molecules readily adsorb to the surface of the sensor. Yet, this process is completely random and the off-target molecules do not bind to the ordered binding sites of the mologram. Thus, their scattering is uniform in all spatial directions and therefore they hardly contribute to the measured light intensity in the narrow solid angle of the focal spot.

Quantification of Molecular Interactions in Living Cells in Real Time using a Membrane Protein Nanopattern


11. June 2020

Molecular processes within cells have traditionally been studied with biochemical methods due to their high degree of specificity and ease of use. In recent years, cell-based assays have gained more and more popularity since they facilitate the extraction of mode of action, phenotypic, and toxicity information. However, to provide specificity, cellular assays rely heavily on biomolecular labels and tags while label-free cell-based assays only offer holistic information about a bulk property of the investigated cells. Here, we introduce a cell-based assay for protein–protein interaction analysis. We achieve specificity by spatially ordering a membrane protein of interest into a coherent pattern of fully functional membrane proteins on the surface of an optical sensor. Thereby, molecular interactions with the coherently ordered membrane proteins become visible in real time, while nonspecific interactions and holistic changes within the living cell remain invisible. Due to its unbiased nature, this new cell-based detection method presents itself as an invaluable tool for cell signaling research and drug discovery.

Principles for Sensitive and Robust Biomolecular Interaction Analysis


28. January 2019

Label-free biosensors enable the monitoring of biomolecular interactions in real time, which is key to the analysis of the binding characteristics of biomolecules. While refractometric optical biosensors such as surface plasmon resonance (SPR) are sensitive and well-established, they are susceptible to any change of the refractive index in the sensing volume caused by minute variations in composition of the sample buffer, temperature drifts, and most importantly nonspecific binding to the sensor surface in complex fluids such as blood. The limitations arise because refractometric sensors measure the refractive index of the entire sensing volume. Conversely, diffractometric biosensors–for example, focal molography–only detect the diffracted light from a coherent assembly of analyte molecules. Thus any refractive index distribution that is noncoherent with respect to this molecular assembly does not add to the coherent signal. This makes diffractometric biosensors inherently robust and enables sensitive measurements without reference channels or temperature stabilization. The coherent assembly is generated by selective binding of the analyte molecules to a synthetic binding pattern–the mologram. Focal molography has been introduced theoretically [C. Fattinger, Phys. Rev. X 4, 031024 (2014)] and verified experimentally [V. Gatterdam, A. Frutiger, K.-P. Stengele, D. Heindl, T. Lübbes, J. Vörös, and C. Fattinger, Nat. Nanotechnol. 12, 1089 (2017)] in previous papers. However, further understanding of the underlying physics and a diffraction-limited readout is needed to unveil its full potential. This paper introduces refined theoretical models, which can accurately quantify the amount of biological matter bound to the mologram from the diffracted intensity. In addition, it presents measurements of diffraction-limited molographic foci, i.e., Airy discs. These improvements enable us to demonstrate a resolution in real-time binding experiments comparable to the best SPR sensors without the need for temperature stabilization or drift correction and to detect low-molecular-weight compounds label free in an endpoint format. The presented experiments exemplify the robustness and sensitivity of the diffractometric sensor principle.

Image reversal reactive immersion lithography improves the detection limit of focal molography


26. November 2018

Focal molography is a label-free optical biosensing method that relies on a coherent pattern of binding sites for biomolecular interaction analysis. Reactive immersion lithography (RIL) is central to the patterning of molographic chips but has potential for improvements. Here, we show that applying the idea of image reversal to RIL enables the fabrication of coherent binding patterns of increased quality (i.e., higher analyte efficiency). Thereby the detection limit of focal molography in bi ological assays can be improved.

Focal molography is a new method for the in situ analysis of molecular interactions in biological samples


25. September 2017

Focal molography is a next-generation biosensor that visualizes specific biomolecular interactions in real time. It transduces affinity modulation on the sensor surface into refractive index modulation caused by target molecules that are bound to a precisely assembled nanopattern of molecular recognition sites, termed the ‘mologram’. The mologram is designed so that laser light is scattered at specifically bound molecules, generating a strong signal in the focus of the mologram via constructive interference, while scattering at nonspecifically bound molecules does not contribute to the effect. We present the realization of molograms on a chip by submicrometre near-field reactive immersion lithography on a light-sensitive monolithic graft copolymer layer. We demonstrate the selective and sensitive detection of biomolecules, which bind to the recognition sites of the mologram in various complex biological samples. This allows the label-free analysis of non-covalent interactions in complex biological samples, without a need for extensive sample preparation, and enables novel time- and cost-saving ways of performing and developing immunoassays for diagnostic tests.

Coherent Signal Picks Out Biomolecular Interactions


11. August 2014

Proteins rarely act alone: Their functioning requires that they establish contact with other proteins and molecules, mostly through noncovalent interactions (i.e., interactions that do not involve the sharing of electrons, such as hydrogen-bond and van der Waals interactions). The study of such interactions is key for the understanding of biology at the molecular level, and may have important implications for drug discovery or the development of diagnostic tests. It is thus crucial to develop measurement techniques that can selectively probe these interactions, characterizing, for instance, the formation rate and strength of a specific protein-ligand complex, while discriminating from other, nonspecific interactions (like those arising, for instance, between a protein and fluctuating solute molecules). Writing in Physical Review X, Christof Fattinger, of Roche Innovation Center, Basel, Switzerland, investigates theoretically a novel analytical method, called focal “molography” (molecular holography), which represents a potential breakthrough for the selective detection of molecular interactions.