Novel iron (III) phthalocyanine derivative functionalized semiconductor based transducers for the detection of citrate

Highlights

• Novel electrochemical iron phthalocyanine derivative based sensors using Si-p/SiO₂/Si₃N₄ and ISFET structures.

• Successful miniaturization process for the semiconductor based transducer.

• Study of the developed chemical sensors performance towards the detection of citrate.

• Wide span linear range of detection (10⁻⁶–10⁻¹ M) with a detection limit of about 10⁻⁷ M.

• Modelisation of experimental data using the enhanced site binding model and TopSPICE ISFET/MEMFET macromedel.

Abstract

In the present work, we report a novel citrate-selective sensor based on iron (III) phthalocyanine chloride-C-monoamido-Poly-n-Butyl Acrylate (Fe(III)MAPcCl-P-n-BA) modified silicon nitride and Ion sensitive field effect transistor (ISFET) structures for the electrochemical determination and estimation of the pathophysiological range of citrate. The developed capacitive sensor based on Fe(III)MAPcCl-P-n-BA had a Nernstian sensitivity of (−20.2 ± 1.3) mV/decade with a detection limit of about 7 × 10⁻⁷ M and a linear range from 10⁻⁶ M to 10⁻¹ M (RSD = 6.2%). Then, the performance of the Fe(III)MAPcCl-P-n-BA functionalized ISFET structure towards the detection of citrate has been investigated. A Nernstian sensitivity of about (−19.8 ± 1.0) mV/decade in the range from 10⁻⁶ M to 10⁻¹ M was achieved (RSD = 4.8%) which covered the pathologically important clinical range of citrate. The detection limit was about 4 × 10⁻⁷ M. The number of available recognition sites N_s and the complexation constant pK were calculated using the enhanced site binding model. A side by side comparison of the developed chemical sensors based on electrolyte-insulator-Semi conductor (EIS) and ISFET structures showed similar characteristics which proves the successful miniaturization of the semiconductor based transducer. The obtained experimental data of the Fe(III)MAPcCl-P-n-BA functionalized ISFET structure were used to validate the TopSPICE ISFET/MEMFET macromodel. The obtained theoretical sensitivity was in good agreement to the experimental one which proves the successful design of the developed ISFET/MEMFET macromodel.

Introduction

Prostate cancer is one of the most frequently diagnosed cancers amongst Western men, as well as men in most developing countries [1]. A serious limitation involved in prostate cancer is the absence of non-invasive and early stage warning procedures. In clinical practice, the most effective method to reduce mortality is the early diagnosis of prostate cancer, which presents few specific symptoms apparent in early stages [2]. In human serum citrate levels are in low concentrations in the range of 0.06–0.14 mM [3]. However, In healthy males, citrate levels in seminal fluid samples are much higher averaging 25.4 [4] to 28.9 mM [5]. But, with men diagnosed with prostate cancer, these values are reduced significantly [6], [7], [8] up to a factor of ten [9], [10]. This characteristic makes citrate a viable early marker for prostate cancer [11], that can provide important information for patient assessment in multiple clinical settings [2]. Indeed, The estimation of citrate from prostate or seminal fluid samples may help assess early stage risks and can indicate the stage, location and tentative form of the malignancy, as well as assisting in follow-up of the disease progression and regression of the malignancy. To date, several analytical approaches have been developed for citrate detection, including Northern blot analysis including ion-exchange chromatography [12], HPLC-UV [13], HPLC potentiometry [14], fluorimetry [15], spectrophotometry [16], [17], [18], chemiluminescence [19], potentiometry [20], [21], [22], [23], [24], [25], mass spectrometry [26], cyclic voltammetry [27], [28], square wave voltammetry [29], amperometry [29], [30], [31], magnetic resonance spectroscopy [32], [33].

Electrochemical sensors constructed by modified electrodes hold a great promise to serve as suitable devices for point-of-care diagnostics [34], [35], [36]. They can allow for a simple, rapid, and inexpensive multiplexed analysis with remarkable detection sensitivity, reproducibility, and ease of miniaturization [37], [38], [39]. They have found a vast range of important applications in the fields of industrial, environmental, agricultural and clinical analyses for the detection of trace amounts of biologically important compounds [40], [41], [42] Indeed, the interest in chemical sensors has shown a considerable increasing during the last decades in order to satisfy the need of chemical, industrial and environmental analyses. Insulator substrate based chemical sensors are widely used because of the interesting role that plays these substrates as a chemical barrier [43]. Electrolyte–Insulator–Semiconductor (EIS) devices are electronic devices that have been developed to measure pH. To extend their affinity for other ions than H⁺, it is necessary to functionalize these structures with sensitive membranes. Silicon dioxide was the most widely used in sensor devices [44], [45]. However, some inherent disadvantages reduce its effectiveness for passivation, its high permeability towards water and other impurities [46]. Subsequently, in order to obtain stable sensors, it is required to use other insulators such as Si₃N₄ which is one of the most interesting for electronic-based biosensors [47]. In fact, silicon nitride offers a number of advantages compared to other materials, such as the absence of undesirable impurities and the excellent control of the film composition and thickness. The combination of its electronic and mechanical properties makes Si₃N₄ within the semiconductor biomedical industry [48]. This is especially important for ultra-thin layers used in gate and tunnel dielectrics in the fabrication of biosensor devices with metal-oxide-semiconductor (MOS) technology. Thus, Si₃N₄ surfaces are extremely attractive material for a wide variety of potential applications and could be used as alternative candidate material in the preparation of ion-sensitive field-effect transistor (ISFET) based bio-chemical sensors, first established by Bergveld [49], that have features of robustness, rapid reaction time, simplicity in fabrication, low cost, high sensitivity, small size and can be implemented by CMOS technology.

Metallophthalocyanines (MPc) are 2-dimensional 18-electron aromatic porphyrin synthetic analogues with a metal atom located at the central cavity. Because of their interesting properties like excellent thermal stability, chemical inertness, photoconductivity and semiconductivity, metallo-phthalocyanine and their polymers have gained importance and attracted a great interest [50]. Their useful properties are attributed to their efficient electron transfer abilities. Metallophthalocyanines were used in many fields including energy conversion (photovoltaic and solar cells) [51], chemical sensors [52], photo sensitizers [53], gas sensors [54], liquid crystals [55], and nonlinear optics [56]. In other side, Metal-phthalocyanine has already found applications in the design of chemical sensors, in particularity to detect toxic anions because of the importance of the metal centre. The anions coordinate as an axial ligand, to the metal centre of the carrier molecule. Iron phthalocyanine and its related complexes have continued to show themselves as attractive organo-metallic functional materials for potential sensing applications [57] since they present excellent catalysts for various chemical and electrochemical reactions [58], [59]. Recently, the enhanced catalytic properties of iron (III) phthalocyanine has been utilised for the determination of some amino-acids and inorganic anions. An electrochemical sensor for the sensitive and selective detection of cysteine is proposed based on gold nanoparticles (AuNPs) – Iron (III) phthalocyanine (Fe (III)Pc) modified graphite paste electrode [60]. The electrochemical detection of nitrite was also achieved via electrodeposition of gold nanoparticles onto glassy carbon electrodes, followed by 3-mercaptopropionic acid (MPA) self-assembly, enabling attachment of an iron (III) monoamino-phthalocyanine (FeMAPc) catalyst via amide bond formation [61].

The main objective of the proposed research was the development of new chemical sensors based on a novel iron phthalocyanine derivative modified EIS and ISFET structures for the detection of citrate ions. The key ionophore was characterized using RAMAN spectroscopy in order to investigate its structural properties. Then, morphological properties have been investigated using contact angle measurements and scanning electron microscopy.