Ultrasensitive Fluorescent Biosensor for Creatinine Determination in Human Biofluids Based on Water Soluble Rhodamine B Dye-Au3+ions Conjugate

A smartphone-integrated portable rotating platform for estimation of concentration level of plasma-creatinine using whole human blood

The measurement of creatinine concentration is performed to monitor the renal health. The devices available in modern clinical laboratories for measuring creatinine concentration are accurate and provide results rapidly but may be prohibitively expensive for resource-poor settings. Therefore, developing an inexpensive yet accurate device for measuring creatinine concentration is needed. Consequently, we developed a simple, affordable, and portable spinning disc for measuring plasma-creatinine concentration with 10 μL of whole human blood. 5 μL of the alkaline picrate solution is loaded into the device and rotated at 1000 rpm to transport this solution to the periphery of the microchannel. Further, 10 μL whole blood is loaded in the same channel and spun at 1300 rpm for 10 min. The creatinine in plasma reacts with alkaline picrate (Jaffe reaction), and the color of the mixture changes to yellow-orange color. The resulting color is captured with a smartphone, and creatinine concentration is estimated using an in-house developed app (CREA-SESE). The value of creatinine measured with the present device and the gold standard device are highly correlated (R² = 0.998). The bias and standard deviation of the difference between the two measurements are 0.134 mg/dL and 0.143 mg/dL. This study demonstrates the feasibility of a simple, inexpensive, and portable rotating device for measuring creatinine concentration using 10 μL of whole human blood, which can easily be deployed to the underserved population in resource-constrained settings to monitor renal diseases.

Insight into mechanisms of creatinine optical sensing using fluorescein-gold complex

Creatinine level in biological fluids is a clinically relevant parameter to monitor vital functions and it is well assessed that measuring creatinine levels in the human body can be of great utility to evaluate renal, muscular, or thyroid dysfunctions. The accurate detection of creatinine levels may have a critical role in providing information on health status and represents a tool for the early diagnosis of severe pathologies. Among different methods for creatinine detection that have been introduced and that are evolving with increasing speed, fluorescence-based and colorimetric sensors represent one of the best alternatives, thanks to their affordability, sensitivity and easy readability. In this work, we demonstrate that the fluorescein-Au3+ complex provides a rapid, selective, and sensitive tool for the quantification of creatinine concentrations in ranges typical of sweat and urine. UV-visible absorption, diffuse reflectance spectroscopy, steady state and time resolved fluorescence spectroscopy were used to shed light on the molecular mechanisms involved in the changes of optical properties, which underlie the multiplexed sensor analytical reply. Interestingly, sensing can be performed in solution or on solid nylon support accessing different physiological concentrations from micromolar to millimolar range. As a proof-of-concept, the nylon-based platform was used to demonstrate its effectiveness in creatinine detection on a solid and flexible substrate, showing its analytical colorimetric properties as an easy and disposable creatinine point-of-care test.

Exploiting a strong coupling regime of organic pentamer surface plasmon resonance based on the Otto configuration for creatinine detection

The sandwiched material-analyte layer in the surface plasmon resonance (SPR)-Otto configuration emulates an optical cavity and, coupled with large optical nonlinearity material, the rate of light escaping from the system is reduced, allowing the formation of a strong coupling regime. Here, we report an organic pentamer SPR sensor using the Otto configuration to induce a strong coupling regime for creatinine detection. Prior to that, the SPR sensor chip was modified with an organic pentamer, 1,4-bis[2-(5-thiophene-2-yl)-1-benzothiopene]-2,5-dioctyloxybenzene (BOBzBT₂). To improve the experimental calibration curve, a normalisation approach based on the strong coupling-induced second dip was also developed. By using this procedure, the performance of the sensor improved to 0.11 mg/dL and 0.36 mg/dL for the detection and quantification limits, respectively.

High stability resistive switching mechanism of a screen-printed electrode based on BOBZBT2 organic pentamer for creatinine detection

The resistive switching (RS) mechanism is resulted from the formation and dissolution of a conductive filament due to the electrochemical redox-reactions and can be identified with a pinched hysteresis loop on the I-V characteristic curve. In this work, the RS behaviour was demonstrated using a screen-printed electrode (SPE) and was utilized for creatinine sensing application. The working electrode (WE) of the SPE has been modified with a novel small organic molecule, 1,4-bis[2-(5-thiophene-2-yl)-1-benzothiopene]-2,5-dioctyloxybenzene (BOBzBT2). Its stability at room temperature and the presence of thiophene monomers were exploited to facilitate the cation transport and thus, affecting the high resistive state (HRS) and low resistive state (LRS) of the electrochemical cell. The sensor works based on the interference imposed by the interaction between the creatinine molecule and the radical cation of BOBzBT2 to the conductive filament during the Cyclic Voltammetry (CV) measurement. Different concentrations of BOBzBT2 dilution were evaluated using various concentrations of non-clinical creatinine samples to identify the optimised setup of the sensor. Enhanced sensitivity of the sensor was observed at a high concentration of BOBzBT2 over creatinine concentration between 0.4 and 1.6 mg dL-1-corresponding to the normal range of a healthy individual.

Optical Supramolecular Sensing of Creatinine

Calix[4]pyrrole phosphonate-cavitands were used as receptors for the design of supramolecular sensors for creatinine and its lipophilic derivative hexylcreatinine. The sensing principle is based on indicator displacement assays of an inherently fluorescent guest dye or a black-hole quencher from the receptor's cavity by means of competition with the creatinine analytes. The systems were thermodynamically and kinetically characterized regarding their 1:1 binding properties by means of nuclear magnetic resonance spectroscopy (¹H and ³¹P NMR), isothermal titration calorimetry, and optical spectroscopies (UV/vis absorption and fluorescence). For the use of the black-hole indicator dye, the calix[4]pyrrole was modified with a dansyl chromophore as a signaling unit that engages in Förster resonance energy transfer with the indicator dye. The 1:1 binding constants of the indicator dyes are in the range of 10⁷ M^-1, while hexylcreatinine showed values around (2-4) × 10⁵ M^-1. The competitive displacement of the indicators by hexylcreatinine produced supramolecular fluorescence turn-on sensors that work at micromolar analyte concentrations that are compatible with those observed for healthy as well as sick patients. The limit of detection for one of the systems reached submicromolar ranges (110 nM).

Fabrication of an improved amperometric creatinine biosensor based on enzymes nanoparticles bound to Au electrode

An improved amperometric creatinine biosensor was fabricated that dependent on covalent immobilisation of nanoparticles of creatininase (CANPs), creatinase (CINPs) and sarcosine oxidase (SOxNPs) onto gold electrode (AuE). The CANPs/CINPs/SOxNPs/AuE was characterised by scanning electron microscopy and cyclic voltammetry at various stages. The working electrode exhibited optimal response within 2 s at a potential of 0.6 V, against Ag/AgCl, pH 6.5 and 30 °C. A linear relationship was observed between creatinine concentration range, 0.1-200μM and biosensor response i.e. current in mA, under optimum conditions. Biosensor offered a low detection limit of 0.1 μM with long storage stability. Analytical recoveries of added creatinine in blood sera at 0.5 mM and at 1.0 mM concentrations, were 92.0% and 79.20% respectively. The precision i.e. within and between-batch coefficients of variation were 2.04% and 3.06% respectively. There was a good correlation (R² = 0.99) between level of creatinine in sera, as calculated by the colorimetric method and present electrode. The CANPs/CINPs/SOxNPs/Au electrode was reused 200 times during the period of 180 days, with just 10% loss in its initial activity, while being stored at 4 °C, when not in use.HighlightsPrepared and characterised creatininase (CA), creatinase (CI) sarcosine oxidase (SOx) nanoparticles and immobilised them onto gold electrode (AuE) for fabrication of an improved amperometric creatinine biosensor.The biosensor displayed a limit of detection (LOD) of 0.1 μM with a linear working range of 0.1 μM-200 μM.The biosensor was evaluated and applied to measure elevated creatinine levels in sera from whom suffering from kidney and muscular disorders.The working electrode retained 90% of its initial activity, while being stored dry at 4 ˚C for 180 days.

Nitrogen-terminated silicon nanoparticles obtained via chemical etching and passivation are specific fluorescent probes for creatinine

A method is described here to prepare water-dispersible nitrogen-functionalized silicon nanoparticles (N-SiNPs). It consists of two steps, viz. etching of the oxidized shell of SiNPs and nitrogen-passivation of the exposed silicon. The resulting N-SiNPs have an average diameter of 2.6±0.7 nm and show blue fluorescence (with excitation/emission peaks at 340/420 nm). The fluorescence quantum yield is 23% and the decay time is in the nanosecond regime. Compared to etching methods using a plasma or hydrofluoric acid, the process described here (etching and passivation) is mild, continuous, fast, and air-compatible. The N-SiNPs modified with chlorotetracycline are shown to be a viable fluorescent probe for creatinine. Fluorescence drops in the 0 to 20 μM creatinine concentration range, and the limit of detection is 0.14 μM.

A Passive Mixing Microfluidic Urinary Albumin Chip for Chronic Kidney Disease Assessment

Urinary albumin level is an important indicator of kidney damage in chronic kidney disease (CKD) but effective routine albumin detection tools are lacking. In this paper, we developed a low-cost and high accuracy microfluidic urinary albumin chip (UAL-Chip) to rapidly measure albumin in urine. The UAL-Chip offers three major features: (1) we incorporated a fluorescent reaction assay into the chip to improve the detection accuracy; (2) we constructed a passive and continuous mixing module in the chip that provides user-friendly operation and greater signal stability; (3) we applied a pressure-balancing strategy based on the immiscible oil coverage that achieves precise control of the sample-dye mixing ratio. We validated the UAL-Chip using both albumin standards and urine samples from 12 CKD patients and achieved an estimated limit of detection (LOD) of 5.2 μg/mL. The albumin levels in CKD patients' urine samples measured by UAL-Chip is consistent with the traditional well-plate measurements and clinical results. We foresee the potential of extending this passive and precise mixing platform to assess various disease biomarkers.

Michael Addition Based Chemodosimeter for Serum Creatinine Detection Using ( E)-3-(Pyren-2-yl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one Chalcone

First, a simple and highly emissive fluorescent chalcone ( E)-3-(pyren-2-yl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (PTP) was synthesized via simple shaking along with an excellent quantum yield of 0.85, and proved as a stable, highly sensitive, and selective biosensor for creatinine. Owing to its unique photophysical interaction with creatinine through Michael adduct formation, PTP was utilized as a Chemodosimeter for the selective recognition of creatinine in blood serum. Under optimized conditions, a broad range of creatinine detection was achieved  from 0.00000113 mg/dL to 15.8 mg/dL along with an excellent limit of detection of 0.00000065 mg/dL (0.058 nM). This biosensor is highly reproducible even for different concentration levels of creatinine. It is the very first creatinine biosensor possessing a wider linear range for clinical applications for creatinine. To ensure its clinical application, blood serum samples of people of different age groups were collected from Alpha Hospital and analyzed for creatinine by using our chemodosimeter method and compared with data obtained using a commercial method in the Alpha hospital. Our data show very good agreement with clinical data. Because clinical protocol involves trienzymes and tedious sample preparation, no doubt, our chemodosimeter will be a cheap and sensitive option compared to the existing clinical methods.