Abstract— In recent years there has been an exploitation of sustainable and environmental-friendly technologies for civil engineering applications. One of the most studied and promising technologies is soil improvement using biocementation through microbially induced calcite precipitation (MICP). MICP occurs due to the enzymatic activity of microbes living or added to the soil, with the analysis of this enzyme allowing a possible method for quantifying the amount of biocement (calcite) produced. This work presents and validates a novel detection tool to quantify and monitor urease in situ by employing a lab-on-a-chip (LOC) device. The device uses magnetoresistive biochips as biosensors in tandem with a read-out electronic set-up, magnetic labels and an integrated microfluidics system. A calibration curve for jack bean urease concentrations of 0.5 mg/mL to 70 mg/mL was obtained, serving as proof-of-concept for future in situ monitorization of biocementation. Experiments comparing direct urease assay detection versus sandwich assays were also conducted, with no difference being found between the two methodologies. I. INTRODUCTION Population and consequently civil infrastructure continue to expand at unprecedented rates. As such, the availability of competent soils for construction, as well as the rehabilitation of existent civil infrastructure are a major concern to meet ever-growing societal needs at minimal environmental impact [1]. Traditional soil and infrastructure reinforcement solutions usually involve the use of cement which is not an environmentally-friendly technique. As such, the harnessing of biological processes in civil engineering emerges as a promising approach, a “green technology”. In case of being used for soil improvement, it can be used to reduce ground permeability and increase stiffness and strength [2]. Biomineralization, in particular microbially induced calcite precipitation (MICP), has been the primary focus of research in biogeotechnical engineering to date. MIPC is the creation of calcium carbonate (calcite) as a consequence of microbial metabolic activity [3]. Calcite precipitation may be achieved by many different processes, of which enzymatic hydrolysis *Research supported by FCT- Fundação para a Ciência e a Tecnologia. D. C. Albuquerque and S. Cardoso are with INESC-MN- Microsystems and Nanotechnologies, Rua Alves Redol, 9 1000-029 Lisbon, Portugal and IST - Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1 1049-001, Lisbon, Portugal (corresponding author: phone: +351213100300 ext:2540, e-mail: debora.albuquerque@ist.utl.pt; e-mail: scardoso@inesc- mn.pt). R. Cardoso is with CERIS/ICIST- Civil Engineering Research and Innovation for Sustainability, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1 1049-001, Lisbon, Portugal (e-mail: rafaela.cardoso@ist.utl.pt). G. A. Monteiro and S.O. Duarte are with IBB–Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1 1049-001, Lisbon, Portugal (e-mail:gabmonteiro@ist.utl.pt; e-mail: sofia.duarte@tecnico.ulisboa.pt). V. C. Martins is with INESC-MN – Microsystems and Nanotechnologies, Rua Alves Redol, 9 1000-029 Lisbon, Portugal (e-mail: vromao@inesc- mn.pt). of urea by urease being the most energetically efficient of all [1]. MICP is uplifted by injecting the soil or medium to treat with nutrients (calcium chloride and urea) and urease producing bacteria, such as Sporosarcina pasteurii [4], to fill pores, flaws and cracks of those materials [5, 6]. The calcite produced is the biocement and has already been used in applications concerning soil stabilization, earth construction, restoration, sealing and remediation [7] [8]. There are, however, some drawbacks of using this technique. The main adversity comes on obtaining a homogeneous distribution of bacteria (and, consequently, calcium carbonate) over the soil [9]. The microbial activity is also dependent of environmental factors like temperature and pH, which can also be a problem. Both affect the amount of biocement produced, and therefore the treatment efficiency. In this context, one of the challenges of biocementation is centered around the performance monitoring, which mostly lies on the assessment of enzymatic activity of urease. Standard enzymatic assays include spectrophotometry, fluorimetry, potentiometry and amperometry. However, these traditional assays are mostly time consuming, require extensive sample pre-treatment, and are unsuitable for in situ implementation [10]. This creates a need for an alternative enzymatic monitorization method for urease, that despite reliable is also able to give in situ information. Lab-on-a-chip (LoC) devices, consisting on integrated systems to achieve automation on sample preparation and user-friendliness for point-of-use operation, could be the answer to this need [11]. In this paper a LoC device consisting of a magnetoresistive platform is tested on the quantification of urease. The LoC apparatus consists then of four main components: biochips with magnetoresistive sensors, magnetic labels (magnetic nanoparticles MNPs), electronic set-up, and a reusable microfluidics system is used as a proof-of-concept. II. MATERIALS AND METHODS A. Biochemical Reagents All reagents used in the biochemical tests were of analytical grade and the water deionized. The anti-Canavalia ensiformis urease rabbit polyclonal antibody biotin-conjugated was purchased from Rockland. Sulfo-LC-SPDP (Sulfosuccinimidyl 6-(3’-[2-pyridyldithio]-propionamide) hexanoate) and BSA (Bovine Serum Albumin) were acquired from Pierce, and urease C. ensiformis (Jack bean) from Sigma-Aldrich. Nanometer sized magnetic particles (250 nm, Nanomag-D) were from Micromod, Germany. The magnetic nanoparticles (MNPs) are 75-80% (w/w) magnetite, coated with dextran and streptavidin-modified, presenting about 1000 binding sites for biotin. They present a magnetic moment of 1.6 x 10-16 A.m 2 for a 1.2 kA/m magnetizing field and a susceptibility of χ ~ 5 [12]. The buffers used were phosphate buffer 0.1 M pH 7.4 (PB) and phosphate buffer 0.1 M pH 7.4 Tween-20 0.02% (v/v) (PB-Tween20). Towards a portable magnetoresistive biochip for urease-based biocementation monitoring* D. C. Albuquerque, R. Cardoso, G. A. Monteiro, S. O. Duarte, V. C. Martins, S. Cardoso