An electrochemical sarcosine sensor based on biomimetic recognition

Development of a highly sensitive fluorescent probe using Delonix regia (Gulmohar) tree pod shell for precise sarcosine detection in human urine samples: advancing prostate cancer diagnosis

We designed a highly sensitive fluorescent sensor for the early detection of sarcosine, a potential biomarker for prostate cancer. This sensor was based on surface-cobalt-doped fluorescent carbon quantum dots (Co-CD) using a FRET-based photoluminescent sensing platform. Blue luminescent carbon quantum dots (CQD) were synthesised through a hydrothermal approach, utilizing Delonix regia tree pod shells. Cobalt was employed to functionalize the CQD, enhancing the quantum-entrapped effects and minimizing surface flaws. To optimize Co-CD preparation, we employed a Box-Behnken design (BBD), and response surface methodology (RSM) based on single-factor experiments. The Co-CD was then used as a fluorescent probe for selective Cu2+ detection, with Cu2+ quenching Co-CD fluorescence through an energy transfer process, referred to as 'turn-off'. When sarcosine was introduced, the fluorescence intensity of Co-CD was restored, creating a 'turn-on' response. The sensor exhibited a Cu2+ detection limit (LOD) of 2.4 µM with a linear range of 0 μM to 10 µM. The sarcosine detection in phosphate buffer saline (PBS, pH 7.4) resulted in an LOD of 1.54 μM and a linear range of 0 to 10 µM. Importantly, the sensor demonstrated its suitability for clinical analysis by detecting sarcosine in human urine. In summary, our rapid and highly sensitive sensor offers a novel approach for the detection of sarcosine in real samples, facilitating early prostate cancer diagnosis.Communicated by Ramaswamy H. Sarma.

A closed-loop catalytic nanoreactor system on a transistor

Precision chemistry demands miniaturized catalytic systems for sophisticated reactions with well-defined pathways. An ideal solution is to construct a nanoreactor system functioning as a chemistry laboratory to execute a full chemical process with molecular precision. However, existing nanoscale catalytic systems fail to in situ control reaction kinetics in a closed-loop manner, lacking the precision toward ultimate reaction efficiency. We find an inter-electrochemical gating effect when operating DNA framework-constructed enzyme cascade nanoreactors on a transistor, enabling in situ closed-loop reaction monitoring and modulation electrically. Therefore, a comprehensive system is developed, encapsulating nanoreactors, analyzers, and modulators, where the gate potential modulates enzyme activity and switches cascade reaction "ON" or "OFF." Such electric field-effect property enhances catalytic efficiency of enzyme by 343.4-fold and enables sensitive sarcosine assay for prostate cancer diagnoses, with a limit of detection five orders of magnitude lower than methodologies in clinical laboratory. By coupling with solid-state electronics, this work provides a perspective to construct intelligent nano-systems for precision chemistry.

Colorimetric paper-based sarcosine assay with improved sensitivity

This manuscript reports on a simple paper-based bienzymatic colorimetric assay for sarcosine as an important urinary biomarker of prostate cancer. All required assay reagents are pre-deposited on hydrophilic filter paper spots surrounded by a hydrophobic barrier. Sarcosine in the sample solution is selectively oxidized in the presence of sarcosine oxidase (SOx), resulting in the formation of hydrogen peroxide, which is subsequently detected through the horseradish peroxidase (HRP)-catalyzed conversion of the colorless indicator 3,3',5,5'-tetramethylbenzidine (TMB) into its blue-colored oxidation product. By the modification of the paper with positively charged poly(allylamine hydrochloride) (PAH), a linear response to sarcosine between 0 and 10 μM and a significant lowering of the limit of detection (LOD) (0.6 μM) compared to the unmodified paper substrate (12.6 μM) has been achieved. The improvement of the LOD was attributed to the fact that the presence of the polymer limits the enzyme-driven colorimetric reaction to the surface of the paper substrate, resulting in stronger color development. In experiments in artificial urine matrix, the bicarbonate anion was identified as an inhibitor of the colorimetric reaction. This inhibition was successfully eliminated through on-device sample pH adjustments with pH-buffer components pre-deposited onto assay devices. The LOD for sarcosine achieved in artificial urine matrix (2.5 μM) is below the 5 μM threshold value for this urinary biomarker required for diagnostic purposes. Finally, good selectivity over all 20 natural amino acids and satisfactory long-term storage stability of reagent-modified paper substrates at - 20 °C for a period of 50 days were confirmed.

Sensors for diagnosis of prostate cancer: Looking beyond the prostate specific antigen

Prostate cancer represents one of the most common forms of cancer affecting men across the globe. Due to late diagnosis of this disease, the mortality of this condition is very high. Conventional diagnostic methods like the direct rectal examination are uncomfortable and, in most cases, delayed, and further confirmation is required with biopsies and Gleason score. The most common biomarker approved by the FDA (United States Food and Drug Administration) is the prostate specific antigen (PSA) that is detected by conventional biochemical assays which require expensive reagents, is time-consuming and more often is only indicative and cannot be considered confirmative as it is susceptible to erroneous conclusions. The prostate health index employs quantification of PSA in its free and bound forms to enumerate the risk of prostate cancer and has found acceptance with clinicians though the methods used to determine these quantities are slow and require additional sensitivity. Search for novel biomarkers other than PSA has resulted in the identification of several promising candidates. However, their detection is still heavily dependent upon conventional biochemical assays that retain the challenges of being time-consuming, poorly sensitive and expensive. Development of specific sensor technologies integrating nanomaterials offers a viable alternative for rapid and sensitive determination of these non-PSA markers. This review summarizes the major advances in the development of sensors for diagnosis of prostate cancer using non-PSA markers. It also highlights some of the emerging paradigms in cancer diagnosis that may transform the diagnostic field in the context of prostate cancer.

Ultrasensitive Ti3C2TX MXene/Chitosan Nanocomposite-Based Amperometric Biosensor for Detection of Potential Prostate Cancer Marker in Urine Samples

Two-dimensional layered nanomaterial Ti₃C₂T_X (a member of the MXene family) was used to immobilise enzyme sarcosine oxidase to fabricate a nanostructured biosensor. The device was applied for detection of sarcosine, a potential prostate cancer biomarker, in urine for the first time. The morphology and structures of MXene have been characterised by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrochemical measurements, SEM and AFM analysis revealed that MXene interfaced with chitosan is an excellent support for enzyme immobilisation to fabricate a sensitive biosensor exhibiting a low detection limit of 18 nM and a linear range up to 7.8 µM. The proposed biosensing method also provides a short response time of 2 s and high recovery index of 102.6% for detection of sarcosine spiked into urine sample in a clinically relevant range.

Adaptable Xerogel-Layered Amperometric Biosensor Platforms on Wire Electrodes for Clinically Relevant Measurements

Biosensing strategies that employ readily adaptable materials for different analytes, can be miniaturized into needle electrode form, and function in bodily fluids represent a significant step toward the development of clinically relevant in vitro and in vivo sensors. In this work, a general scheme for 1st generation amperometric biosensors involving layer-by-layer electrode modification with enzyme-doped xerogels, electrochemically-deposited polymer, and polyurethane semi-permeable membranes is shown to achieve these goals. With minor modifications to these materials, sensors representing potential point-of-care medical tools are demonstrated to be sensitive and selective for a number of conditions. The potential for bedside measurements or continuous monitoring of analytes may offer faster and more accurate clinical diagnoses for diseases such as diabetes (glucose), preeclampsia (uric acid), galactosemia (galactose), xanthinuria (xanthine), and sepsis (lactate). For the specific diagnostic application, the sensing schemes have been miniaturized to wire electrodes and/or demonstrated as functional in synthetic urine or blood serum. Signal enhancement through the incorporation of platinum nanoparticle film in the scheme offers additional design control within the sensing scheme. The presented sensing strategy has the potential to be applied to any disease that has a related biomolecule and corresponding oxidase enzyme and represents rare, adaptable, sensing capabilities.

Quantitative analysis of sarcosine with special emphasis on biosensors: a review

The quantitative determination of sarcosine is of great importance in clinical chemistry, food and fermentation industries. Elevated sarcosine levels are associated with Alzheimer, dementia, prostate cancer, colorectal cancer, stomach cancer and sarcosinemia. This review summarizes the various methods for quantitative analysis of sarcosine with special emphasis on various strategies of biosensors and their analytical performance. The current bio sensing methods have overcome the drawbacks of conventional methods. Sarcosine biosensors work optimally at pH 7.0 to 8.0 in the linear range of 0.1 to 100 μM within 2 to 17 s and between 25 and 37 °C, within a limit of detection (LOD) between 0.008 and 500 mM. The formulated biosensors can be reused within a stability period of 3-180 days. Future research could be focused to modify existing sarcosine biosensors, leading to simple, reliable, and economical sensors ideally suited for point-of-care treatment. Clinical significance Elevated sarcosine levels are associated with prostate and colorectal cancer, Alzheimer, dementia, stomach cancer and sarcosinemia. Quantitative determination of sarcosine is of great importance in clinical chemistry as well as food and fermentation industries. Attempts made in development of sarcosine biosensors have been reviewed with their advantages and disadvantages, so that scientist and clinicians can improvise the methods of developing more potent sarcosine biosensor applicable in multitudinous fields. This is the first comprehensive review which compares the various immobilization methods, sensing principles, strategies used in biosensors and their analytical performance in detail.