This is a sufficient length for a possible single-use consumable

This is a sufficient length for a possible single-use consumable. 1.3) 10?4 RIU to (3.2 0.7) 10?5 RIU. We discuss the influence of the region of interest (ROI) size around the achievable LOD. We fabricated a biochip by combining a microfluidic and a PCS and exhibited autonomous transport. We analyzed the performance via refractive index actions and the biosensing ability via diluted glutathione S-transferase (GST) antibodies (1:250). In addition, we illustrate the velocity of detection and demonstrate the advantage of the additional spatial information by PX 12 detecting streptavidin (2.9 g/mL). Finally, we present the detection of immunoglobulin G (IgG) from whole blood as a possible basis SEDC for point-of-care devices. Keywords: photonic crystal slab, label-free, point-of-care, microfluidics, PX 12 biochip 1. Introduction Label-free biosensing is usually a PX 12 promising platform for inexpensive and easily available point-of-care (POC) devices [1]. Due to the absence of labeling, the handling is usually greatly simplified, which enables use by untrained personnel. Furthermore, the quick availability of specific panels of biomarkers is usually of great importance for the assessment of a patients health. For instance, Cardenas [2] has shown that assessment of the thrombin levels of trauma patients helps in predicting the development of serious complications during their hospital stay. In addition, Apple et al. [3] have shown that checking troponin levels of emergency room patients suffering from myocardial infarction reduces their length of stay in hospital. Moreover, the epidemic of SARS-CoV-2 has shown how quickly the demand for easy-to-use and readily available point-of-care testing devices might emerge [4]. Zanchetta et al. [5] pointed out in their review that label-free sensing allows detection of the binding behavior in real time and potentially enables the detection of small molecules, as occluding molecules due to labelling are omitted. Finally, label-free platforms are versatile, enabling a wide range of applications. Label-free sensing has been studied on platforms such as electrical, electrochemical, mass-sensitive, or optical transducers [6]. In this work, we focus on optical transducers. Label-free sensing with optical transducers has been demonstrated with surface plasmon resonance (SPR) [7], ring resonators [8,9], slot waveguides [10,11], and photonic crystal slabs (PCS) [12,13,14]. Here, we focus on PCS. A PCS is usually a nanostructured waveguide commonly processed on a solid substrate such as glass. Upon illumination, the nanostructure acts as a grating coupler and diffracts light that satisfies the Bragg equation into the waveguide. The light propagates along the waveguide as a quasi-guided mode. Due to the grating, light is usually coupled back out and leads to constructive and destructive interferences in reflection PX 12 and transmission, respectively. This leads to guided-mode resonances (GMR) in the spectrum [15,16,17]. The behavior is usually described by is the Bragg mode integer [18,19]. We analyze first-order behavior and set = 1. The electrical field distribution of the guided mode is not confined to the boundaries of the waveguide [20,21]. It has exponential components, which decay into the superstrate and substrate. These fields are called evanescent waves and extend approximately 50 nm to 100 nm out of the waveguides [22,23,24]. This renders the PCS sensitive to changes of the refractive index at the surface. Any change of refractive index leads to a shift of the guided-mode resonance of the PCS, as shown in Equation (1). Different options exist to track resonance changes. A common approach is based on spectrometric readout [25,26,27,28]. While a spectrometer enables a chromatic resolution, it is usually a rather bulky instrument and a significant cost factor for point-of-care applications. A compact alternative is based on a photodetector or camera-based readout as was shown by Lin et al. [29], Kenaan et al. [30], and Jahns et al. [31,32]. Lin et al. [29] and Jahns et al. [31] used the system response of their setups to translate the chromatic shift into an observable change of intensity. In this case, the system response is the light emitting diode (LED) spectrum and the GMR lies on the falling shoulders of the LED. Any change in resonance position leads to a change of intensity and is thus detectable by camera or photodiode. However, they reported moderate limits of detection (LOD) in the range of 1 1.48 10?4 RIU [29] to 3.36 10?4 RIU [32]. The limit of detection is defined as the triple noise level divided by the sensitivity. It is commonly estimated by the expression LOD.