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Despite major advances in biosensing, quick, dependable, and effective on-site detection of bacterial infections remains a serious issue, owing to a lack of acceptable or appropriate diagnostic platforms. To address this gap, we presented a new colorimetric gold NanoZyme aptasensor for rapid sensing of Aeromonas veronii, an infectious bacterial disease in fish. The A. veronii-specific aptamer (AVS01) was developed through Cell-SELEX. The sensing mechanism involves inhibition of AuNPs induced peroxidase-mimic catalytic activity through surface adsorption by AVS01 which in the presence of the A. veronii desorb from the AuNPs allowing recovery of the catalytic activity leading to colorimetric response, whereas the sensor is insesnsitive to other nontarget bacterial cells. This method is very specific and sensitive, allowing for the quick and visible sensing of A. veronii with a detection limit of 1281 CFU mL−1 within 15 min. The method has great potential for rapid diagnosis of bacterial infection in fish caused by A. veronii.

Hexavalent chromium or Cr(VI) is highly toxic for humans as it causes high oxidative reactions inside cells, leading to diseases like chronic ulcers and damage to the kidneys, mucous membranes, throat, skin, and respiratory tract. Due to rapid urbanization, Cr(VI) comes into our food chain through unmonitored and uncontrolled application in agriculture fields, refineries, mills, the tanning industry, automobiles, road works, etc. Presently, the standard Cr(VI) detection is done using conventional processes, which, though accurate, has severe drawbacks in on-the-spot rapid detection in the field. Here, we have represented a handheld potentiostat towards trace-level Cr(VI) detection in aquatic environments. A Cr(VI) specific DNA aptamer immobilized screen printed electrode (SPE) has been used as the main biosensor. The device operates on an electronic peak current dumping event through mass deposition in the presence of an aptamer coupled with Cr(VI) onto the working electrode. The working range of the developed prototype is in the range of 0–1000 ppb Cr(VI), where the maximum linearity has been observed in the range of 0–500 ppb with a limit of Detection (LOD) as low as 10 ppb. The device has exhibited an excellent correlation with commercially available electrochemical workstations with a coefficient of 0.972. Moreover, the applicability of the developed device has been validated for 7 different types of water samples. To our knowledge, this is the first-ever reported simplistic resource-limited on-spot aptasensing device for Cr(VI) detection in an aquatic environment.

Acetylcholinesterase (AChE), a widely used enzyme for inhibition-based biosensors in pesticide residues detection, lags due to multiple-step operation, time-consuming incubation and reactivation/regeneration steps. Herein, this endeavour reports the development of Organophosphate Hydrolase (OPH), which has functional superiority over the AChE and explored in on-spot biosensing device for organophosphate pesticide residue detection in fruits and vegetables. The organophosphate degrading enzyme OPH is expressed from the ‘opd’ gene through biotechnological tools. The OPH exhibited its best activity at pH 8.0 and subsequently thermal inactivation over 37 °C. The activity of the purified OPH enzyme was found 2.75 U mL−1 at λmax 410 nm. Furthermore, the developed OPH is integrated into 96 well plate format with our previously reported UIISScan 1.1, an advanced imaging array technology based field-portable high-throughput sensory system. The developed biosensor revealed a linear range from 100 ng mL−1 to 0.1 ng mL−1 for detection of organophosphate pesticide residues with a negative slope i.e. y = 235.678x (ng mL−1) – 62.8725 with R2 = 0.99991 and n = 23. Moreover, the applicability of the developed biosensor was tested for market available fruits and vegetables. This is the first-ever reported OPH mediated on-spot biosensing device for pesticide residue detection in fruits and vegetables to the best of our knowledge.